correct pH tablets and danios

Question
I have some danios in a 5 gallon tank (how many is too many?) and I want to know if I can put Correct pH tablets in the tank while the fish are in there.  I cleaned out the fishtank (3/4 of it) yesterday and today I found one of the fishes dead.

Answer
Hi Jenny;

Your fish were used to the old water and when such a large quantity of new fresh water was added they went into shock so that's probably why the one died. Water conditioner is very important too. A good one removes chlorine/chloramine and helps the fish with stress. Use it every time you change or add water to your tank.

Organic wastes cause your tank water to change over time and new water can be very different from the old. Partial weekly changes of 25% with gravel vacuuming are important to keep your fish healthy. It keeps the water chemistry more stable. Trying to alter the pH more now will make the fish more stressed and more of them could die so don't add any of the tablets. It's best to just leave the pH alone anyway. Trying to alter it even under normal circumstances can cause fluctuations that can be deadly to your fish. They will get used to whatever the pH tends to be in the tank and with the weekly 25% changes they should be just fine. Adding water for evaporation doesn't count. You have to remove water and replace it in order to keep the fish healthy.

A 5 gallon tank can safely house about 5 danios as long as there is good filtration. If you have more than 5, make two water changes a week to keep the water chemistry and water quality more consistent. The general rule of thumb for small fish like danios is one inch of fish per gallon. Some danios get larger than an inch so you should research the type you have to see how big they get.

At Your Service;
Chris Robbins