View Full Version : tap water for water changes

08-19-2016, 10:02 AM
Last week I had to do a large (65%) water change in my big tank (50 g). I had enough conditioned water to make up about 45% but had to add about 20% of fresh tap water. (I checked the temp after the water change and it was 75 deg. F. so there was no big drop in water temp) Well, the following day I found my previously healthy pearl gourami dead on the bottom of the tank. There were no other deaths. What is the general advice about using fresh tap water for water changes?

(P.S. the water changes were because I am following the advice to use praziquantel for gill flukes. I am doing that because of "glancing" behavior of fish which started after I added new fish to the main tank). At this point I changed the water, as indicated above, and will wait the required 5 days before changing 25% of the water and adding the second and final dose of praziquantel.)

As usual I am grateful for your help!

Larry Bugg
08-19-2016, 10:24 AM
Did you use something to remove the chlorine like prime? I certainly don't think this water change had anything to do with the death. It simply wouldn't have been that quick. Because I keep discus, I do daily large water changes, sometimes up to 100%. I normally age my water for 24 hours but there have been many times that I didn't have enough aged and used tap water. Even a temp difference shouldn't be a problem. It is also not unusual for me to do changes with a 6 to 8 degree lower temp to induce breeding. Never been a issue.

08-21-2016, 07:28 AM
Sorry ... double post

08-21-2016, 07:29 AM
A temperature difference may not be the only difference between your tank water and the tap water, whether aged 24 hours or new. Larry pointed out that the death may be coincidental, which is quite possible. It should also be pointed out that his daily water changes of up to 100% ensures that the "old" tank water will be nearly identical to the new water. However, if it has been some time since the most recent water change prior to the water change you just did, it is likely that there could be a substantial difference between the old water and the new water. Hardness and pH are two notable parameters. The aquarium is a closed system, so parameters can change slowly over time. Excess food can cause pH to change as it decomposes. Some gravel and decorations can cause the hardness to change. Fish waste and plant waste dissolve in the water, feeding bacterial colonies, which have their own waste products. Parameters can change slowly, and the fish may acclimate to the slow change. Then along comes a massive water change, and the new water is way different in one or more parameters (temp, pH, hardness, etc.), causing stress. In some cases, the stress is a positive inducement for breeding (or other behavior) to occur, while in other cases, it can overload their capability to rapidly acclimate to the new conditions, up to and including death. Other factors are the overall general health of fish, the age, and size. Of course some species are more sensitive than others.

Was the 20% tap water you added treated to remove chlorine and/or chloramine before it was added? You do not mention treating the unaged tap water. The chlorine found in municipal water systems should not be introduced into an aquarium. If you can't age it, a few drops of chlorine remover can age tap water in a few minutes, preferably before it is added to the tank.