Hi. The problem I have is that I’ve lost most of my fish following treatment with praziquantel. Tank details: 200 litres, community tank. Heated to 24, filtered with a Hydra 40 (Maidenhead Aquatics). It’s been a problem free tank and is 8 months old, planted well and has a mix of kuhli loach, guppy, neon tetra and both red cherry and amano shrimp. Around 18 fish in total, 4 amano and a bunch of red cherry who bred very easily. Lighting 0700-2200 and all has been well. A couple of weeks ago, I noticed some of the fish brushing their gills against the tank contents, there was some fin reddening and fins had a feint white edge on some fish. Research led me to a diagnosis of gill fluke. Further research indicated over the counter treatments could harm shrimp so ‘Fluke Solve’ seemed to be the answer (praziquantel 50%). 0.8g was added a week ago... the following day I noticed the fish struggling a bit and within 24 hours lost a couple of guppies, this was followed by a kuhli loach and a number of red cherry shrimp. Over the last few days the death rate has been soul destroying. None of the neons or amano have died. I can’t find anything to reference regarding these problems with the use of fluke solve, the manufacturer is not able to advise. The treatment requires a second dose but I’m concerned this will finish everything off. Advice from local aquarium stores is to stop. Readings are the same as normal, PH = 7.2, nitrates = near to 0, nitrites = 0, ammonia = 0. As the fish remaining seem to be heading to the top a lot, I thought it must be low dissolved O2 as the problem. The filter disturbs the surface and I added an air stone to increase this. I generally rotate water changes with RO and tap water (treated) - 30 litre water changes every week with a bigger change once a month. I used RO with minerals yesterday as I’m running out of ideas. I have less than 10 fish left, only 1 kuhli left from 4 and he has red, sore looking gills and if he comes out briefly, swims erratically, towards the top. I have a black guppy with a fan tail, the edges are white / jagged and condition of the tail has deteriorated over the day. One other point, the plants in the tank appear to be struggling since the treatment too, some dying leaves on the java fern and crypt. Moss is thinning out and much more straggly. A lot going on I know.... any suggestions on what to do next would be gratefully received.
I think, for the foreseeable future, ensuring that water quality is kept good (ammonia and nitrite at 0, nitrates at no more than 20 above tap water level) is key. I wouldn't treat with further medication but instead focus on consistent water quality alone. The addition of the air stone was a good plan too. Best of luck that this helps the tank to settle down.
I notice you have a mix of hard water (guppies) and soft water (neon tetras) fish - one or the other may not fare as well generally (unless you've somehow customised the RO to be appropriate for the requirements of all fish*) and it might be that the medication sent them over the edge. * https://www.seriouslyfish.com/knowledge-base/ will tell you the hardness/softness requirements for each species.