Water change about KO'ed my tank!

[weezer]

I did a water change last night. Two 25% changes back-to-back. Within about 1 hour all my fish were at the top of the tank trying to breath air from the surface! About three hours later they were starting to become more active and this morning everything was back to normal.

Whoa! What have I done? I can't imaging that the O2 concentration had dropped that drastically. Any ideas?

Thanks,

Weezer

 

[Jchillin]

Two things come to mind: Water temp and/or dechlorinator. O2 is definitely not a part of it, since the water going in creates a saturation.

Was the temp of the new water the same? Did you add dechlorinator? I assume you used buckets, hence the two in a row. Going forward, it would be better to do 50% at one time.

 

[weezer]

I used a python. 25% gets me down to the top of the heater and thats as low as I dare go. Dechlorinator was not used. I never thought it would be a problem with such a small water change.

Guess I have learned otherwise!

 

[Zagz]

Always use dechlorinator and if you want to do more pwc at a time, unplug the heater until you have refilled with water of the same temp. Remember to plug it back in though!

 

[Japola44]

Remember to plug it back in though!

yes plug it back in! I always seem to have the problem of not remebering this until i wake up in the middle of the night after doing a water change. Its happened 2 times in a row

 

[BrianNY]

Another potential hazard when doing pwcs are pH swings. I would advise testing the pH straight from the tap vs the tank. Sometimes tap water contains a fair amount of CO2. As the CO2 gasses out, it elevates the pH. If your tank has a low pH to start with, it can result in a violent swing which stresses fish.

 

[7Enigma]

You need to monitor your ammonia and nitrIte readings for the next several days. It's very possible some chlorine that was in the tap water could have killed your beneficial bacteria in your filter. Always use dechlorinator unless you are sure your tap water contains no chlorine or chloramines.

Also, I'd recommend not just adding the dechlor and dumping it right into the tank. Use a hand or net to stir the water for a minute or two to distribute the dechlor throughout the water, and make sure the temp is the same as the tank water.

 

[petunia100]

I have had this happen to me also when using a python. I used dechlorinator, by fish that stayed by the end of the python started gasping, while those at the other end of the tank were okay. I added extra dechlorinator and everyone recovered in about 15-20 minutes. I learned it is important to wait between emptying and refilling to let the dechorinator spread around the tank. Or to stir it around a bit before filling.

 

[TomK2]

I know some who beleive that a 25% PWC without a dechlorination method would be OK, but I do not recommend it. The theory is that the chlorine is rapidly diluted and aerated out of the tank for smaller water changes. Dechlor is cheap and effective, with virtually no downside, so why skip it. However, Chloramine is not removed by aeration, and not adding dechlor to chloramine water would be bad. very bad.

 

[BillD]

I am one who believes you can do 25% pwc without dechlor. This is assuming a normal level of chlorine in the tapwater, somewhere less than 3ppm. The theory may be that it will gas out, and it may in time, but the fact is that the chlorine will react almost instantly with any organics in the water. It will be gone in minutes, not by out gassing, but by oxidizing organics which is how it works. It is an exytremely powerful oxidizing agent. However, it is better to remove the chlorine, because of the byproducts of this oxidation. One thing that happens in the winter here (but may not be a factor in Texas, is that the water becomes supersaturated with air, and the resulting air bubbles that come out of the water when it warms is sometimes problematic for fish. The bubbles may be to small to be seen, but can cause distress to a fishes gills. So, it is too much O2, not too little.