Possible tank problem, perhaps disease?

Question
Hello there,

I have a big problem on my hands and I have no clue as to what it may be. I have a 20 gallon tank in which I used to have a flourishing guppy community. Last year, I unfortunatly fell ill and did not care for the tank as I should have. My guppies seemed to have survived that stage however, and were doing fine until two weeks ago.

Two weeks ago I cleaned out the whole tank, like I do every summer. I adjustade temperature and water PH, then put the fish back in. Everything was fine. Then, 5 days later, I bought a pleco (mine had died last year) and 8 new female guppies (my males were outnumbering the females). This is when things started getting out of hand. I lost one of my new ones that very night, and another the next day. 3 days later, I left for a five day trip and upon my return had lost two more of my new fish and three of my own.

I have been back for 3 days and every day I have lost one or two more of my fish. All my males are dead now, the rest are still juveniles with the exception of my 4 new adults. I do have babies in the tank. I have checked the water quality and everything is fine with the exception of a slightly high PH level (it was 7.6 last night and is now 7.4. Been treating that the way the test kit said to). The fish don't look ill, with the excpetion of one showing slight dulleness in colours.

I do have one problem with the tank though: we are in the middle of a big heat wave and the water temperature went up while I was away. It's been 86F in the tank since I came back and it just won't go down because it is so hot the appartment. Is it possible I am actually "cooking" my fish? If the temperature is the problem, how do I bring it down safely?

I am very concerned. Thank you for your time.
Sincerely,
Nathalie L'Ecuyer

Answer
hi nathalie

you should never ever clean the whole tank. i think thats the main problem why your fish keep dieing.
by cleaning the whole tank you cleaned up all the good bacteria living in there to help the fishes. you should only do weekly, removing about 20-30% of the water. if you find your tank a little dirty use gravel cleaner to remove some of the waste. make sure you check your amonia and nitrate level. if it's too high do about 30% water change.

fot the temperature what you want to do is, if you have a airconditiner put it on, it will cool the tank down. other thing you could do is get a small fan and put it on the top of the tank it will lower your temperature down.