I was wondering if anyone could help me find out what is going wrong with my Blue Eye Fork tail Rainbow fish.I had three of them but i have lost a male this way. I have them (breeding pair) in my community tank for about 6 months and were doing really well until the last few months they have been acting strange. The female is losing weight and kinda panting, and scales kinda sticking out (but not like dropsy). I had few but they have all died this way. Is there anything i can put in my tank to help? I have used Furan 2 but the fish died about 3 hours later. My tank water is testing fine and I'm doing fortnightly water changes. All my other fish in the tank are doing fine! I'm wondering if the local council has been putting other stuff in out tap water which fish are reacting to. I used to use tap water up till one died this way (i looked round for info about this problem but i cant not fine anything). Since that i have been using RO water. It has helped but i topped up my tank with tap water twice and the rainbow fish has got sick again. What can it be? What can i do to stop it?

Im wanting to get some more of these amazing looking fish but i cant not find them anywhere.

My tank water is testing fine

What is "fine"?

AFAIK many rainbows prefer harder more alkaline water than the typical "community aquarium" with wood, plants, tetras etc. Also I'd increase the water changes to weekly rather than fortnightly, less accumulation of waste = better.

Tested the water yesterday and it came out as PH -7.5 KH - 7 NO3 - 0 NH4 - 0 PO4 - 0. The tank is 150 Ltr and is fully planted with a bit of wood. I have black neon tetra, dwarf chain loach, rummy nose tetra, male fighter, spotted danios and flying fox and a GBA. Other people i know are having problems with some there fish also