[AquaticLife] help again..=(
What do you mean by “left some charcoal floating”?
If you have a master test kit to test for ammonia, nitrites and nitrates, you could use your test results to give you an idea of how frequent you will need to do PWC’s. Try to stick with 25% PWC’s although 1/3rd isn’t bad. Try to avoid large PWC’s unless it’s an emergency since you could change the water parameters too much, too fast, which can cause shock issues to your fish. Do you have a master test kit or any kind of tests?
You’re not a murderer… well, not unless you go to the store where you got the fish and strangle the people there for giving you such bad advice. 
Lenny Vasbinder Fish Blog - http://GoldLenny.blogspot.com
Category: Philippines Internet Koi Society
