Question: Water quality

I have got a bit of a riddle for you

I have a Walstad tank that has been running for about 3months now, it contains 4 species of snail(red ramshorn, zebra nerites, malaysian trumpets and the annoying tiny pond snails), red cherry shrimp, hyalella azteca, asellus, daphnia, copepods etc And of course H.orientalis larvae.

The tank has not had one single water change, just top ups with aged water. I started up this tank packed with egeria densa to remove nitrates and kept it so for about a month then I started planting. Algae came after removal of the egeria but is kept under control by the various algae eaters.

I have noticed that the ramshorn and the trumpets are not breeding as they should, however the pond snails are so there's no lack of calcium. Daphnia and the other crustaceans are breeding well so water quality seems ok in that sense. However, the shrimp are dying...

I noticed a pregnant shrimp with fungus on her eggs the other day(normally they can fight off fungus), she died. Then two more young ones this morning. So the question is what are red cherries sensitive to that crustaceans are ok with? Might very well be that the shrimps are just more sensitive. I also suspect that the low reproduction rates of the trumpets and the ramshorn are telling me something.... Unfortunately I did a large water change when I found the dead shrimps this morning before thinking of doing water tests.... All the larvae are well, no problem there.

Any similar experience or ideas?

Riddle solved, it was a temporary spike in nitrates...
I had to feed the critters for the first time about a week ago since the zebras ate up all the algae(damn efficient at algae eating!), tank isnt used to that kind of high end nutrients(newt chow...stupid me...) so nitrates went up. Apparently shrimp are extremely sensitive to nitrates..

Still stupified regarding the slow reproduction rates of the trumpets and ramshorn though.. That is more of a long term problem to be honest. Especially the trumpets..

I suppose what you've written about nitrates explains why cherry shrimps never did well for us. We had a couple of batches and they lived long enough but whenever they had eggs, they lost them before they hatched. We had high nitrates in tap water but it seems to have improved now so I might try getting shrimps again. I don't have any snails but ostracods never seemed to mind the water quality.