I'm rescuing a tank I recently acquired care of. I've never done this before so not confident on my next move. The tank I acquired is a 125 gallon freshwater. 3 fish. 1 id shark. 2 other little fish. No plants. Aqua clear 110 filter. Heater probably doesn't work. My water readings are: PH:7.0 Kh: 180 Gh:300 No2:.5 No:200 I don't think the water was changed for a while so I've done two 10% water changes in 3 days.. I've read you can shock them with too much fresh water? And should I be using a conditioner for hard water?? Fish seem kinda happy except for Id shark just hides all day. Would plants help stabilize the tank also?? Sorry lots of questions... search only finds so much.