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Old 04-14-2005, 11:40 PM   #1
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Deaths after water change

I have had a 30 gallon community tank with a variety of easy, hardy fish doing well. I recently did a water change, using distilled water. This water change may have been a little larger than usual. I do not change the Whisper biobag when I do a water change. I usually wait to do that at another time.

Shortly after, both of my little gold dust mollies and the cobalt dwarf gourami died around the same time. None of the other fish...platies, rasbora, orange dwarf gourami, clown loaches...had any problems at all.

Any ideas about what happened? I have used distilled water for most of my water changes for quite a while, with no prior problems.

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Old 04-14-2005, 11:43 PM   #2
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Do you add water change chemicals when you do your water changes?
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Old 04-15-2005, 12:55 AM   #3
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Also, distilled water has no buffering capacity & is prone to pH drops. Perhaps the pH in the tank had drifted down & the water change now cause a big pH change & shock the fish.

BTW - to avoid pH problems, it is generally recommended to add some kind of buffer to distilled or RO water - either salts you can buy from the lfs, or cc, or some source of carbonates.
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Old 04-15-2005, 01:12 AM   #4
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how much did you change?
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Old 04-15-2005, 08:40 AM   #5
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I'm a proponent of water changes. The thing is the parameters of the new water MUST be close to the old water. This is even more crucial when doing large changes. Otherwise the fish (and even worse), the nitrifying bacteria will succumb to a sudden pH swing.
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Old 04-15-2005, 09:54 AM   #6
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I agree with the above - even "bad" water can't be replaced in large quantities because the sudden change is so hard on the fish and bacteria.

What is the reason for using distilled? It lacks a lot that the fish need, so if you are concerned about water quality out of the tap a better choice might be spring water, or at least mix the distilled with your tap water.
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Old 04-15-2005, 03:47 PM   #7
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Thanks. Ive always used distilled for my saltwater tanks, and at some point assumed it would be good for the freshwater tanks as well. Maybe Ive just been lucky averting disasters. I will mix it with tap water next time, at least for the freshwaters.
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Old 04-15-2005, 03:52 PM   #8
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Distilled water lacks important trace elements. When you use it for s/w tanks, you are mixing it with the salt which contains the necessary trace elements. Therefore in the s/w, you want to control every element possible. You start with nothing in the water (using distilled or ro/di) and add only desired elements.

For your fresh water tank, if you don't want to use a basic dechlorinator mixed with tap water, just use spring water.
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Old 04-16-2005, 12:06 AM   #9
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Thanks, all, for the thoughtful advice. I will start using a mixture of dechlorinated tap and distilled water, gradually moving to more tap.
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change, deaths, eat, water change

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