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Iron Oxide (cement dye)


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Anyone know about using iron oxide for coloring.

Is it safe to use?

Does it affect pH... etc?

I've done some experimentation with mixing some of the dye with silicon glue and sand.

The colors and textures have turned out extremely well smile.gif

I am now ready to "decorate" my "rockwork" with this mixture.

But, before I do, can anyone tell me if this dye is safe to use in this way?

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I don't speak from experience but only from my knowledge of studying chemistry at university.

Iron Oxide is an extremely stable compound but when you intoduce it into water there will be some part of the iron that is converted into free iron (Fe2+). I doubt whether the iron will have too much effect on your fish but if you soaked your rock work for a week or so and then did regular water changes (2-3 times per week) once the iron oxide products are introduced I think your fish should be ok.


recently I made some caves by rolliing a piece of pvc pipe in silicon and then coating it with fine gravel - it also looks really good. Fish have been just fine.

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Speaking of silicon, what sort do you use?? i have had a look around and there are so many choices.

Would you be able to give me some brand names that are good, that are suitable for using on rocks etc and will stay together underwater, as alot of silicons are not recommended for permenant water submersion, in this case the fish tank.



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For the silicone read the tube and make sure that it is aquarium safe, otherwise its bye bye fishies..

If anyone knows of specific brands they could tell you what they works well for them..

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Laterite which is a clay based rock from the tropic and sub-tropics contains large amounts of iron oxide. It is one type of substrate that is used in planted tanks as the laterite increases the cation exchange rate within the tank. The laterite stores the nutrients until the plants are able to use them. The iron oxide as far as I know has little affect on the fish within the tank. The chemical industry has developed synthetic oxides so you may have to read the label to find out if it is real deal. I have a book at work that may put some more light on the matter so I will add more tomorrow.


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If it is the stuff used by concretors for stamping concrete. I think it would pay to be carefull. I just went and looked at my tub of "black" oxide(coloured iron oxide) I use for marking and it has chemicals(nitrobenzene) in it. I'm guessing to pad it out or make it cheaper to manufacture?

If it sealed in silicone though wink.gif , I'm not prepared to guess???



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Hi Dave (EB),

Any acetic cure silicone is suitable for aquarium use. There are several brands available ...Selleys, GE and Dow Corning are common brands. Contractors grade will suffice unless you need a stronger bond..in which case use construction grade.

Ed...I have used iron oxide to colour cement in aquariums and havenot had any problems. As has been mentioned, fill and drain your tank a few times to flush the excess. Also you can buy a Fe test kit if you want to check it before adding the fish.

merjo smile.gif

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Ok thanks to all. You have all been so helpful.

I love this forum wub.gif

Eddie: the stuff I have does not mention nitrobenzene at all.

here's what it says on the container

Australian Builders Oxide Powder is a resilient, high quality Iron Oxide.

Australian Builders Oxide Powder has no added fillers, extenders or binders.

It is free of soluble matter and never cakes or deteriorates.

Its purity and fineness gives Australian Builders Oxide Powder maximum colour staining power.

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hey the best silicone ive found is rodersil v2 its sticks quick but so be carefull

and dont quote me on spelling


I won't: laugh.gif

Rhodorsil V2, Acetic Cure, High Performance Glazing Silicone by Rhodia

St George uses this stuff and it's awsome.

I have used it to repair live tanks. As long as the area you are glueing is 100% dry (i.e. clean it with metho and a fan) it will cure when exposed to humidity very quickly.

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