problems with new bleeding heart tetra
5 weeks in on new 10 gallon planted tank. I have been out of the planted tanks for 7 years so I am a little rusty. The problem is I have liquid rock for my tap. 400 ppm Gh, High Kh. I did not want to use R/O but the water is way to hard for fish & plants I want to keep. Mistake #1 I brought in fish to cycle the tank while cycling a backup 10 gallon for quarantine purposes. The first batch died 2 yellow danios , found out later they had gill flukes from store. Then I brought in 2 bleeding heart tetras. 1 died first week looked like it had mouth fungus, he was treated in hospital tank but died anyway. The planted 10 gallon tank in question has 6 different plants & flourite substrate with pressurized Co2 with 3 watts per gallon. Small external power & small sponge filter. Gh 10, Kh 5, ph average 7.0. Co2 runs only with lights so I get some ph swing. Temp average 78.5 F. I dose with flourish, flourish Fe, plantex with CSM+ boron, some calcium at times,& potassium nitrate. I keep a close watch on Ph, GH, Kh, Po4, NO3, NO2, NH3,NH4. I thought the tank was stable all nutrients chem levels including ammonia , nitrite, were gone with a slight 0.10 or less of nitrite & plants were lifting the top off the tank. Even the 1 lone bleeding heart was doing well. Now I picked up a nitrite spike at 0.25 & rising & the last bleeding heart going on a hunger strike & hiding the corner but does come out & seems interested in eating though. A week ago I treated the fish for gill flukes because some scratching against plant leaves, I contribute that to fertilizer but could still have gill flukes. My question is , is the problem gill flukes or is the fish hiding more for other reasons like tank still cycling??? I still use 20 % tap & remineralize remaining r/o, also I use prime. Sorry for long post but background info needed. Any Ideas?