Fish deaths after water changes

[LeighBeigh]

To my great dismay, I have lost all but one of my African cichlids, and three clown loaches also survived ( I had mixed varieties of cichlids in a 200 litre tank) after doing a water change. I had put extra Prime in the fresh water due to where we live and the time of the year as I had been previously instructed by a fish enthusiast. I live in the Goulburn River area in Victoria. I tested the water in the tank after the tragedy and the pH was fine, no nitrates or nitrites, no amonia, temperature was fine. Any ideas why this should happen? Some of my fish were quite large as I had had them for a number of years and up until then had been healthy. 

I have since put six small cichlids into the tank and they are thriving. When I bought them, I asked the guy in the shop who seemed quite knowledgeable. He asked if I had done the water change on a Friday. I couldn't remember when, but he said "they" dump loads of chemicals into the water on Fridays and that was probably what had killed my fish. He said to do water changes early in the week so the chemicals have evaporated. Does anyone know if this is true? I don't have access to any other water, except tap water. Any tips on dong water changes would be appreciated. I really don't want this to happen again! 

[Link2Hell]

Sorry to hear mate

It is not uncommon for the local water board to add chemicals to the water supply if they feel there is a problem or

as a routine to avert a possible problem hence that Friday in your area is a problem day

Sydney water have done that in the past up here and they don't notify they are doing it

the fish will react to this and first signs they are unhappy are flashing were they rub against anything in the tank,

they all hang at the water line breathing heavy or just go into spirals

you need to invest in a water drum that way you can adjust the water parameters and have it run for a few day with

an airstone or pump before you use it so it turns over

drum size is up to you and dictated by position usually, close to a power point is good, you will also need a pump

and some hose to reach from the drum to the tank and position the drum where you have a stable temp otherwise

you may need to add a heater if the weather is cold or just boil the kettle and add to get the temp up

make sure the plastic drum has only had something safe to humans in it and has a lid like in the pic

 

 

[Ageofaquariums]

Generally this happens because the aquarium is refilled higher than normal, this reduces the surface agitation resulting in very little oxygenation. Because most dechlorinators reduce oxygen levels it becomes a double wammy. Not saying it wasnt bad water, but the tests didnt pick up anything obvious and in my experience lack of oxygen is the more likely cause.

[PlecoSam]

How much water did you change?

At what point did you add the dechlorinator, i.e. bucket or tank?

 

[Ageofaquariums]

The fact the loaches survived makes it unlikely this was a poisoning or chloramine burn situation imho. Loaches go down hard in that scenario. Whereas coming often from hot oxygen poor waters, they have an edge against cichlids when o2 is low.

 

[humbug]

I agree with your reasoning AoA. 

One thing though – although it’s often spoken about, I really do wonder just how much water conditioners deplete oxygen in a tank.  Yes – I understand the chemical reactions involved, but I suspect that in a tank with reasonable water movement the oxygen is very quickly replenished by diffusion at the water surface.

One instance that really brought it home to me was when I inadvertently picked up the bottle of Seachem Safe instead of the buffer during a water change.  I accidently dosed two tanks with something like a 170x overdose.  It was a while before I realised my error.  The tanks were Malawi cichlid tanks with moderate to heavy stocking, and reasonable water circulation.  Absolutely no impact could be seen on the fish . . . . not even flashing.  I did another large water change to be safe, and all was fine.  The fish are all still going great guns two years later.  I use this not only as an example of how little impact the product seems to have on oxygen depletion, but also just how safe the product is for our fish.

[Ageofaquariums]

Its not just the product that reduces the oxygen content of the water, but the reaction that takes place when it meets chlorine/chloramine. Once the chlorine is gone, the impact on oxygen content is much less dramatic, even tho sulfur-based chemicals are oxygen scavengers that will lower the dissolved oxygen. The situation becomes much worse the less surface agitation there is. Most of us use dual sources of aggressive oxygenation, and are able to restock oxygen as quickly as it is removed. We certainly provide more than the water is able to hold at the temperatures we keep tropicals. The complications in working it out WITHOUT a DO meter (disolved oxygen) is that companies jealously guard the exact chemical used in their products....  and that makes working out the chemistry almost impossible. For the ones using sodium thiosulphate we have the numbers of course    

To quote wiki.

 

Quote

In pH testing of bleach substances, sodium thiosulfate neutralizes the color-removing effects of bleach and allows one to test the pH of bleach solutions with liquid indicators. The relevant reaction is akin to the iodine reaction: thiosulfate reduces the hypochlorite (active ingredient in bleach) and in so doing becomes oxidized to sulfate. The complete reaction is:

4 NaClO + Na₂S₂O₃ + 2 NaOH → 4 NaCl + 2 Na₂SO₄ + H₂O

Similarly, sodium thiosulfate reacts with bromine, removing the free bromine from solution. Solutions of sodium thiosulfate are commonly used as a precaution in chemistry laboratories when working with bromine and for the safe disposal of bromine, iodine, or other strong oxidizers.

 

[Ageofaquariums]

The best data I could find for you was here,  http://www.vita-d-chlor.com/specs/awwarfdechlorguides.htm

 

 

Quote

Dissolved Oxygen. When no dechlorination chemical was added, the dissolved oxygen concentration of the released water decreased from 11.08 to 10.81 mg/L (0.27 mg/L) after traveling 450 feet in one test, and from 10.4 to 10.3 (0.1 mg/L) in a second test (data not shown).  When stoichiometric amounts of dechlorination chemicals were added, the DO decreased by 1.18, 0.3, 0.55, 0.5 mg/L in the presence of sodium metabisulfite, sodium sulfite, sodium thiosulfate and calcium thiosulfate, respectively.  When, twice the stoichiometric amounts of dechlorination chemicals were added, the dissolved oxygen concentration decreased by 1, 0.9, 0.9, 0.7 mg/L in the presence of sodium metabisulfite, sodium sulfite, sodium thiosulfate and calcium thiosulfate, respectively.  With the addition of stoichiometric concentrations of ascorbic acid and sodium ascorbate, the DO of the water increased by 0.3 mg/L, after a travel of 450 feet.  When twice the stoichiometric concentrations of these chemicals were used, the DO decreased by 0.2 mg/L.  The reasons for the trends observed using either concentrations of ascorbic acid and sodium ascorbate are not known.

 

In summary, results indicated that sodium metabisulfite had a greater impact (1.0 – 1.18 mg/L depletion) on the DO concentrations of the water tested.  Sodium sulfite, sodium thiosulfate and calcium thiosulfate decreased the DO concentration by 0.3 to 0.9 mg/L, depending on the amount of dechlorination chemical used.  Ascorbic acid and sodium ascorbate had the least impact on the DO of the water tested.