I had to do an emergency water change last night. Found this- a nerite upturned, not closed properly, with a shrimp moving in. I lifted it out- there was no foul odor, but the operculum fell off so I think it was dying.
Tested water quality- 40ppm nitrates and 0.25 ammonia. I put the snail in a cup of water on top of the tank (for ambient warmth) but don't expect it to live. Did a 50% water change and removed most of the ambulia stems which are fast decaying and littering the tank with needle-like foliage. Maybe that's also a problem- too many dying plants... Didn't re-dose any ferts. Plants are pearling, tank looks a lot cleaner, and all my kuhlis seem to appreciate the fresh water- they are actively exploring all over the tank. Second water test showed lower nitrates- around 30ppm but ammonia the same.... This morning ammonia tests at zero, nitrates are still around 30 and zero nitrite. So I think the issue is resolved.
One of my new kuhlis seems to have sores or fungus on its head. I don't know if it's the same thing affecting the cherry barbs. Hoping the water changes will help it.