Order of Sump Filter Media

[malawi4me]

Hi all..

Quick question for the filter experts!

I have a sump ready to run on a freshwater african tank and have a heap of media and Im wanting to know what order to put the media in, by that I mean the order that that the water flows through in the sump after it leaves the tank to be filtered.

I have...

a few hundred bio balls

4 liters of matrix (seachem)

white filter mating

course filter mat (aqua one)

.........................................

thanks in advance!

Rob.

[mcloughlin2]

The way I would run it would be course filter mat, bio balls, matrix, white filter matting.

Course filter mat - removes larger solid particles to prevent waste build up on biological filtration which would decrease there effectiveness.

Bioballs - supports aerobic bacteria that convert ammonia -> nitrite -> nitrate

Matrix - supports aerobic bacteria aswell, however has the potential to support anaerobic bacteria which convert nitrate to nitrogen gas which exports nitrate from the system.

White filter wool - removes the really fine floating particles so helps contribute to making the water crystal clear.

[malawi4me]

The way I would run it would be course filter mat, bio balls, matrix, white filter matting.

Course filter mat - removes larger solid particles to prevent waste build up on biological filtration which would decrease there effectiveness.

Bioballs - supports aerobic bacteria that convert ammonia -> nitrite -> nitrate

Matrix - supports aerobic bacteria aswell, however has the potential to support anaerobic bacteria which convert nitrate to nitrogen gas which exports nitrate from the system.

White filter wool - removes the really fine floating particles so helps contribute to making the water crystal clear.

Awsome thanks for the reply! Exactly the answer i was after!

[cpfc]

Can I ask why white filter matting (which I presume is fine mechanical filtering) is last and not after course filtering?

[mcloughlin2]

It's just the way I tend to run my filters. It would work fine if it were placed after the course sponge, however it tends to do a better job polishing off the water if it is placed after the water passes through all the filtration media as it filters any sludge that builds up on biological filtration.

[CThompson]

The order should be

• Course filter mat
• white filter wool
• Bio balls or Matrix (possibly dependent on sump design*)

Water should be as clean as possible before it gets to biological media. If you want to put more mechanical after the bio section, that’s fine, but get it clean before otherwise the bio section will become a de facto mechanical.

It should be pointed out that some of this can be dictated by the sump design, which has not been detailed. *Bio balls need to placed in the system so they are not immersed. If sump design does not allow this another bio media is best used.

however it tends to do a better job polishing off the water if it is placed after the water passes through all the filtration media as it filters any sludge that builds up on biological filtration.

I don’t understand the logic behind this comment mate . If it builds up on the biological filtration, that implies it is stuck. If the bio media is now in addition, mechanical filtration media, it’s not going to allow filter wool to do a better job polishing the water, as the dirt is attached to the bio media. Place another layer of filter wool after the bio section by all means, but the best place for wool to go is immediately after the coarser media.

[tangka]

Hi Craig

Im in the process of setting up a sump aswell and would be doing the following.

1 coarse matting

2 fine filter wool

3 bio balls/matrix

Then

i was thinking another layer of fine filter wool to polish the water and even purigen or a similar product. my qestion is if purigen, where is best to place it? in the final chamber before the pump? is there a better product or is it needed? i wont be having any driftwood in my tank so tannin isnt a problem.

cheers

daniel

[malawi4me]

A few more Q's...

Bio balls are supposed to be above water level in the sump correct?

Reason I ask is because in my sump it seems half of the balls will be above the water level and half of them will be immersed. Does this mean the immersed ones wont do their job? If so then why do they bother putting them in some internal filters and cannister filters? Anyhow Im running matrix as well as the Bio balls and have more matrix than what they recommend for my tank size so hopefully this will be good enough.

I think ill go the course mat....then fine...bio balls and finally matrix. This sound OK ?

[CThompson]

The underling basics behind this general topic is really simple.

1) Mechanical media is to strain the water of its rubbish.

2) Biological media is to provide a home for nitrifying bacteria.

If you put 2 first, it becomes a de fecto mechanical as it’s the water’s first point of contact;

Bacteria need three things to live, a surface area, a food source and oxygen. Limit one or more of these factors and you limit their potential beneficial effects. So, if you place 2 before number 1, it will pick up more crud. This will coat the bio medias surface and potentially limit the bacteria’s access to oxygen. Will this limitation affect the life of the fish so detrimentally that they will die? It would be very unlikely – but why plan in and organise a limitation in your filtration?

Regarding bio balls; following on from the above, one of the three things they need is a surface area. That is real estate. All any biological medias are, is a surface area. To really simplify it, more area = better bio media because it can house more bacteria, potentially removing a limitation should your fish colony be big enough.

Bio balls have one of the smallest surface areas of the bio media we use, I think perhaps that it is most likely the smallest. However, bio balls, if set up in a trickle situation are the best bio media you can use, contra to the fact they have the smallest surface area. Why is that? It is because they increase the tank’s O2 exchange footprint. That is, in a trickle situation, they are an oxygen surface area where the CO2 and O2 can exchange with the surface – that is, MORE oxygen gets into the water. AND in addition, MORE O2 is available to the bacteria, removing this potential limitation (remember the three things nitrifying bacteria need?) This is ONLY true if run in a trickle situation. Submerged they haven’t got access to extra oxygen and only what is dissolved in the water – the same as any other biological media, all with a larger surface area. So submerged they have their smaller surface as a limiting factor, and another biological media is better suited.

When something goes wrong with your tank, of the dozens of different factors that can contribute to that, taking I guess a more holistic view and simplifying it down; Fish will die from lack of oxygen before they will die from ammonia poisoning. So all thing being equal, with a fully cycled tank, the added benefit of trickling bio balls outweighs their downside of a smaller surface area, which incidentally can easily be overcome with the addition of more bio balls (provided there is room).

Tangka;

If you have understood the principle behind what I have written, the best place to put purigen is where it will be the least likely to get dirty as a coating of crud may limit its chemical process. Is there a better product? As far as I know it is very good, others may comment on this, but my question to you would be; is it needed at all?

Malawi4me, bioballs are a waste of space when put into a canister. Unless the canister is one of those ones that fill and empty with water and air. So why are they used in canisters other than these? Because people don’t understand the above.

You order is fine, just make sure the bio balls stay moist but not submerged.

Craig

[malawi4me]

The underling basics behind this general topic is really simple.

1) Mechanical media is to strain the water of its rubbish.

2) Biological media is to provide a home for nitrifying bacteria.

If you put 2 first, it becomes a de fecto mechanical as it’s the water’s first point of contact;

Bacteria need three things to live, a surface area, a food source and oxygen. Limit one or more of these factors and you limit their potential beneficial effects. So, if you place 2 before number 1, it will pick up more crud. This will coat the bio medias surface and potentially limit the bacteria’s access to oxygen. Will this limitation affect the life of the fish so detrimentally that they will die? It would be very unlikely – but why plan in and organise a limitation in your filtration?

Regarding bio balls; following on from the above, one of the three things they need is a surface area. That is real estate. All any biological medias are, is a surface area. To really simplify it, more area = better bio media because it can house more bacteria, potentially removing a limitation should your fish colony be big enough.

Bio balls have one of the smallest surface areas of the bio media we use, I think perhaps that it is most likely the smallest. However, bio balls, if set up in a trickle situation are the best bio media you can use, contra to the fact they have the smallest surface area. Why is that? It is because they increase the tank’s O2 exchange footprint. That is, in a trickle situation, they are an oxygen surface area where the CO2 and O2 can exchange with the surface – that is, MORE oxygen gets into the water. AND in addition, MORE O2 is available to the bacteria, removing this potential limitation (remember the three things nitrifying bacteria need?) This is ONLY true if run in a trickle situation. Submerged they haven’t got access to extra oxygen and only what is dissolved in the water – the same as any other biological media, all with a larger surface area. So submerged they have their smaller surface as a limiting factor, and another biological media is better suited.

When something goes wrong with your tank, of the dozens of different factors that can contribute to that, taking I guess a more holistic view and simplifying it down; Fish will die from lack of oxygen before they will die from ammonia poisoning. So all thing being equal, with a fully cycled tank, the added benefit of trickling bio balls outweighs their downside of a smaller surface area, which incidentally can easily be overcome with the addition of more bio balls (provided there is room).

Tangka;

If you have understood the principle behind what I have written, the best place to put purigen is where it will be the least likely to get dirty as a coating of crud may limit its chemical process. Is there a better product? As far as I know it is very good, others may comment on this, but my question to you would be; is it needed at all?

Malawi4me, bioballs are a waste of space when put into a canister. Unless the canister is one of those ones that fill and empty with water and air. So why are they used in canisters other than these? Because people don’t understand the above.

You order is fine, just make sure the bio balls stay moist but not submerged.

Craig

Thanks CT very good info there! will take it on board and apply it to my sump project!

[tangka]

thanks craig

ill show you my sump when complete

cheers

daniel

[Topogigio]

This is a really great thread (along with this too) and I must admit even though I’ve been aware of the whole “course to fine” order of things for many years, I’ve always used fine filter wool first cause it was easy & my LFS does it too (once it gets dirty enough it gets thrown out)…. Now my question to you the filtration expert is what bio media you would recommend for my set-up – I’ve taken onboard what was already written above & allowed the following:

• ~10 litres of:

• 2 layers of green course matting (AquaOne), PLUS
• followed by 1 layer of fine filter wool

ALL of this sits above the water line in an 18 litre clear bucket from bunnings

• ~ 20 litre volume of space (submerged) where I have been tossing between:

Ceramic rings, orLava rock from nursery, or*Any other bio media you recommend

• ~ 5 litres of matrix (submerged)

• ~ 5 litres of fine sponge (like used in cushions) to polish the water & act as the final bio media

• ~ 20 litre volume for a pant refugium, with a bed of “Fluorite” & maybe an el cheapo LED light

• Heater & Return pump: MaxFlo, 6000lph

This sump (1500x430x450H) will run 2 tanks (1800x900x500H & 900x600x700H) and obviously I want to run it as economically as I can (for both my conscious & wallet) and as heavily stocked as I can…. The tank will be predominately neo-tropical cichlids, so the ~20 litres of bio media required will need to be inert – can someone PLEASE help, and yes I know I wrote WAY too much.

Anyways,

Thank you reading

[CThompson]

I've always used fine filter wool first cause it was easy & my LFS does it too (once it gets dirty enough it gets thrown out),

Whether you use it first or last, it will get dirty, and will need to be disposed of, so in fact the "easier" way is to have it second as some (?)larger particulate matter will be caught (theoretically) on the coarse media and not get to the finer stuff which subsequently will take longer to block and need replacing less often. So in fact it is easier to have it in the correct order. Will it make a huge difference? That'll depend on how much larger stuff there is floating around in your tank, and how coarse the coarse media is.

For example, something between bio matt and filter wool in coarseness would be good, if you've the room you could have three different mechanical media. My big tank has four;

Eheim's effisubstrate, kama harda bio matt, white filter wool and Aquasonic blue polishing matt.

Regarding your comment about your LFS; they are just people too, and being on the other side of the counter doesn't mean they are going to be correct.

This stuff is not rocket science, I regard it as really basic simple common sense, but people get confused and make it more complicated than it is, so regarding me being a filtration expert

I'll do my best to respond to your question, it's a bit hard to discern were the question marks are, but you by no means have been verbose, you've just made it hard for me to answer succinctly.

I don't know what "neo-tropicals" are. But fish are fish and regarding this generic filtration topic, the answer should not vary dependant fish type.

I would say here that it is not best practice to stock as heavily as you can. No matter how well and cleverly set up, given a long enough period of time, something WILL go wrong, and maxing out the stocking will compile the issue.

• Ceramic rings, or

I don't know what these are. Are they biological media? I assume so, but I am not familiar enough to know their surface area.

• Lava rock from nursery, or

These are crap with a poor surface area. Perhaps some value where it can be shovelled in in larlge enough quantities. I have been informed, given long enough it binds and forms one solid lump (in a pond situation).

• *Any other bio media you recommend

It's pretty hard to go past Matrix. Pond Matrix is better because the individual matrix pieces are bigger lending themselves more to denitrification.

~ 5 litres of fine sponge (like used in cushions) to polish the water & act as the final bio media

With enough Matrix this will be superfluous and get dirty faster as it will pick up all the crude the mechanical has missed (because it is so fine0. It will block and slow the whole system and you will have to remove all the Matrix to get to it. I'd not use it, but you could consider using it or a similar fine product (Auasonoic blue polishing matt) under your layer of filter wool.

• ~ 20 litre volume for a pant refugium, with a bed of "Fluorite" & maybe an el cheapo LED light

This might be more complicated than you realise, I don't know how much you know about aquatic plants . Grow plants like duckweed (hi Rod) as they are less difficult to grow than submerged plants. In the end, will 20 litres be big enough for a maxed out tank stocking wise? Fish people like gadgets and getting their head in a system so maybe you could do this for your interest, but I wouldn't bother. They will most likely need more than a el cheapo LED light to prosper, and to get your max benefit you must have them growing well and not just eking out an existence.

Regarding heaters; you want you sump to be designed, or at least for the heaters to go in a space where the chamber they are located in can not run dry.

~20 litres of bio media required will need to be inert

Commercial bio media will all be inert so I,m not sure of the understanding behind this comment.

How the actual sump is set up can be critical to how effective the whole system works regardless of media order and type, and an 18 litre clear bucket may not meet these standards. I would suggest you draw up a diagram and add it to the thread so I can see it, if you want.

You might want to look at the denitrate thread that has been discussed recently.

Hope that helps,

Craig

[Topogigio]

I would say here that it is not best practice to stock as heavily as you can. No matter how well and cleverly set up, given a long enough period of time, something WILL go wrong, and maxing out the stocking will compile the issue.

Yes - now that i think about it, you are right here, this is not a good idea.

I don't know what these are. Are they biological media? I assume so, but I am not familiar enough to know their surface area

they look like these, and by reading a little more into them, i realise they are more mechanical than biological - so there goes that idea.

These are crap with a poor surface area. Perhaps some value where it can be shovelled in in larlge enough quantities. I have been informed, given long enough it binds and forms one solid lump (in a pond situation)

i didnt know this; interesting.

It's pretty hard to go past Matrix. Pond Matrix is better because the individual matrix pieces are bigger lending themselves more to denitrification.

Ideally yes i would love to fill this dedicated bio-filtration section of 20 litres of space with matrix, but this stuff is just so damn expensive.... that is why i figured i could use an alternative like ceramic rings (which i now know is not optimal) or lava rock... followed by 5 litres of matrix (which i read is more than enough for the volume of water i'm filtering).... if the price is right may just bite the bullet and get 20 litres worth of matrix

With enough Matrix this will be superfluous and get dirty faster as it will pick up all the crude the mechanical has missed (because it is so fine0. It will block and slow the whole system and you will have to remove all the Matrix to get to it. I'd not use it, but you could consider using it or a similar fine product (Auasonoic blue polishing matt) under your layer of filter wool.

Why i didn't think of that?... im doing this as soon as i get home.

This might be more complicated than you realise, I don't know how much you know about aquatic plants . Grow plants like duckweed (hi Rod) as they are less difficult to grow than submerged plants. In the end, will 20 liters be big enough for a maxed out tank stocking wise? Fish people like gadgets and getting their head in a system so maybe you could do this for your interest, but I wouldn't bother. They will most likely need more than a el cheapo LED light to prosper, and to get your max benefit you must have them growing well and not just eking out an existence.

Taken on board.... will definitely get some plants that can live both in & out of water, like water sprite or milfoil (if they are not illegal), and of course get a decent light.

Commercial bio media will all be inert so I,m not sure of the understanding behind this comment.

the comment was aimed at say non-commercial media people used (like lava rock or coral rubble - which i know will push my ph & kH levels through the roof)

How the actual sump is set up can be critical to how effective the whole system works regardless of media order and type, and an 18 liter clear bucket may not meet these standards. I would suggest you draw up a diagram and add it to the thread so I can see it, if you want.

will try and get a photo up soon, and pick your brain a lil' bit more

You might want to look at the denitrate thread that has been discussed recently.

I must admit this has always been an interest, but never really looked into it thoroughly... i may just have to.

anyways,

thank you for your input,

Omar

[Topogigio]

As promised here are some shots of my sump in question, it looks a little messy, but this will change as soon as the cannister running in tandem goes - CRITICISM most welcome.

*

First up (following everything i have re-learned on this post) is the "Mechanical Chamber":

This now holds more like 15 litres of mechanical media, since the addition of the foam.

Please note that although the photo shows the white filter foam last, this IS NOW CURRENTLY sandwiched between the green matt & foam.

Directly below this mechanical chamber is "free" space of at least 20 litres where im still deciding what put in there. I was contemplating bio rings (ceramic rings) but i feel this wont give me enough biological area. Please note this will always be below the water level

*

Second shot shows more space set aside for more biological media. ~ 5 litres of Matrix (still to put in there / buy; followed by 8 litres of fine foam as a final polisher & media

*

This 3rd shot shows where i plan to make a refugium; photo also shows where both heaters lie - horizontally.

*

Full Sump Shot

*

Full System Shot

I hope this clarifies some of my writings earlier as photos really do speak a 1000 words...

Anyways, thanks for reading

[CThompson]

This threads got the legs of a centipede!

Let me point out, that even if you got everything back to front regarding this topic, it still won't "KILL" your fish. It just isn't clever, that is, why do it wrong if you can just as easily do it better?

Topogigio,

Something that I thought was clarified above; These bio rings which you refer to, the Eheim product is NOT a biological media. It is a mechanical media. It is coarser again than bio mat, and in the order of mechanical media, should be place first, before the bio mat (if the bio mat is being used as a mechanical media).

In your situation, I'd give the efimech ("bio rings in your words) a miss as it would be very difficult to set up. They are usually used as a first point of mechanical contact when the water is coming from below (as with canister filters).

I can't see what the black stuff is under your containers of coral rubble. Square bio balls? If that's the case, as mentioned above, they are best placed in a trickle situation and if not another bio media is best used.

If your plastic bucket covered the area of the first chamber better there would be room for a second above water level bucket where the bio balls could be placed out of the water. You might want to think about making a double Perspex container to fit inside itself in this first chambers area to maximise the chambers footprint and to allow removal of mechanical section while leaving bio balls alone. I can see you are restricted by the end reinforcing bracing, so perhaps two of the same buckets one inside the other, with the bottom of both drilled as a drip tray.

You have more bio mat than is required in this first chamber/bucket. Is it three pieces?

Here's a suggested improvement for what you have;

• one layer of bio mat (used for mechanical media)
• White filter wool
• one layer of bio mat (used as a separator between filter wool layers to help water flow (as the wool gets dirty) not as mechanical media.
• 2nd White filter wool (you'ld be surprised at how much stuff this layer will get)
• one layer of bio mat (used as a separator between filter wool and sponge to help water flow (as wool gets dirty) not as mechanical media.
• Sponge
• Further; if you make the suggested double Perspex/bucket chambe, there may (?) be enough above water level area to have the bio balls (in the bottom of second chamber).
• The water in this below bio balls area (in sump) could be a settlement area where debris that has still gotten though could (dependant on water flow) just settles on the bottom of the tank/sump. The problem with this is the siphon access to clean it, but if you make the double Perspex/bucket chamber this could be lifted out and set to one side to gain access to the bottom.

Just looking at the photograph again, I wonder what sort of access you have to remove this bucket from the sump with the plumbing right on top of it (does it swing out of the way?)

To get better buffering benefit with the coral rubble it would be better spread out, perhaps in the next chamber, but what pH do your fish require? I don't see any Africans.

Pump is better put in line not submerged. If the sun hits the metal of the garage door when it is closed, in summer it will PUMP heat into the garage, and with the tanks right behind the door they will cop it full in the face. The immersed pump can only add to this.

Has this been set up here for long? Have you had high temperature problems in the past?

[Topogigio]

Hello Craig, apologies for taking so long to get back to your input, but here i go;

Re: "ceramic rings" - yeah agree with you there mate, they are mechanical, so they wont be any use for my purposes.

I can't see what the black stuff is under your containers of coral rubble. Square bio balls? If that's the case, as mentioned above, they are best placed in a trickle situation and if not another bio media is best used

you have good eyes mate, they are indeed square bioballs... my plan was to have the whole section filled with bioballs (submerged) BUT then i read this thread - and it opened my eyes to everything i was doing wrong.... so those square bioballs will go.

If your plastic bucket covered the area of the first chamber better there would be room for a second above water level bucket where the bio balls could be placed out of the water. You might want to think about making a double Perspex container to fit inside itself in this first chambers area to maximise the chambers footprint and to allow removal of mechanical section while leaving bio balls alone. I can see you are restricted by the end reinforcing bracing, so perhaps two of the same buckets one inside the other, with the bottom of both drilled as a drip tray.

May look into this as it sounds good... all i need is a couple of extra 40mm elbows & another square bucket, and Im cooking

You have more bio mat than is required in this first chamber/bucket. Is it three pieces?

no, just 2 layers/pieces - but they do take up a lot of space, from memory they are AquaOne green matting.

Here's a suggested improvement for what you have;

• one layer of bio mat (used for mechanical media)
• White filter wool
• one layer of bio mat (used as a separator between filter wool layers to help water flow (as the wool gets dirty) not as mechanical media.
• 2nd White filter wool (you'ld be surprised at how much stuff this layer will get)
• one layer of bio mat (used as a separator between filter wool and sponge to help water flow (as wool gets dirty) not as mechanical media.
• Sponge

I'll try, but like i said, its only 2 layers of bio matt (3 layers i believe will simply not fit), so i may have to customise the above improvement to 2 layers of bio matting only

Further; if you make the suggested double Perspex/bucket chambe, there may (?) be enough above water level area to have the bio balls (in the bottom of second chamber).

Yes i do plan on doing this... you think using Matrix in a trickle situation will be a better alternative to bio balls? or do you think this is not required, as ~5 litres of matrix will already be in use - submerged.

The water in this below bio balls area (in sump) could be a settlement area where debris that has still gotten though could (dependant on water flow) just settles on the bottom of the tank/sump. The problem with this is the siphon access to clean it, but if you make the double Perspex/bucket chamber this could be lifted out and set to one side to gain access to the bottom.

this "settlement area" you talk about, i like this idea BUT, and this is a big BUT.... Do you think the advantages of this settlement /particle trapment SUPERSEEDS the benefits of say using the area to house "bio media"?

Just looking at the photograph again, I wonder what sort of access you have to remove this bucket from the sump with the plumbing right on top of it (does it swing out of the way?)

Yes, all the plumbing is irrigation type, so nothing is glued/siliconed, just hand tighten + teflon

To get better buffering benefit with the coral rubble it would be better spread out, perhaps in the next chamber, but what pH do your fish require? I don't see any Africans.

Well to be honest, the coral rubble in those containers are there to stop the square bioball from floating - stupid i know.... also initially they were going to go in the chamber next to the final foam polisher (where the matrix will be now)

I plan to keep mostly Central American cichlids, but this is up in the air at the moment - if i can find the elusive G. balzanii it will be a predominately South American tank.

Pump is better put in line not submerged. If the sun hits the metal of the garage door when it is closed, in summer it will PUMP heat into the garage, and with the tanks right behind the door they will cop it full in the face. The immersed pump can only add to this.

Has this been set up here for long? Have you had high temperature problems in the past?

I plan on clading styrofoam sheeting on both the sump & tanks' sides in summertime just to alleviate the heat issue (behind this set-up is another 6x2x2 saltwater setup thats lived through 2 summers with no problems)

The set-up is very young less than 6 weeks.

thanks for all your help.

[CThompson]

no, just 2 layers/pieces - but they do take up a lot of space, from memory they are AquaOne green matting.

AquaOne green matting – bio mat – kama harda biomat = all the same thing as they are all the same.

Yes i do plan on doing this... you think using Matrix in a trickle situation will be a better alternative to bio balls? or do you think this is not required, as ~5 litres of matrix will already be in use - submerged.

Bio balls surface area is external (why their convoluted shape). Matrix's surface area is principally internal (Buy Pond Matrix by the way as they are bigger particles and will lend themselves more to denitrification that the smaller standard sized Matrix).

This means the bio balls have a greater surface area that is external = in contact with the air = removes O2 as a limiting factor to bacteria growth and increases O2 exchange= better than Matrix where they have most of their surface internal = not in direct air contact.

this "settlement area" you talk about, i like this idea BUT, and this is a big BUT.... Do you think the advantages of this settlement /particle trapment SUPERSEEDS the benefits of say using the area to house "bio media"?

There will be stuff that is not filtered out, and it will settle somewhere.

Biological media is best placed after all the mechanical stuff has been done (as explained), but that doesn't mean it has to go IMMEDIATELY after it. Anywhere after it but before pump.

Suck it and see, look to see where the settlement goes, perhaps put a screen of biomat as a barrier between sections to slow the rush (but not block) the water between the sections before the bio media.

Well to be honest, the coral rubble in those containers are there to stop the square bioball from floating - stupid i know.... also initially they were going to go in the chamber next to the final foam polisher (where the matrix will be now)

I have just used sufficiently heavy but small pieces of sandstone to do this. What you are doing is fine, other than the fact it will buff the water.

[Topogigio]

thanks mate... your input has really got me thinking in the right direction.... i hope to have a killer sump when i'm done - it'll be patented as the Thompson2000 series