Hello Nick,
just wanted to sympathise with losing the shrimp. I’m gutted for you. I can’t really bring anything to the table that the very experienced guys on here have already but having read the whole thread I would humbly offer the following if for no other reason than at this point than by my reckoning you have little to lose; (This from a guy that can’t grow plants, that collects different genera of algae like football stickers but has a seemlingly healthy and gently growing community of blue neos for now by luck more than judgement). Caveat emptor.
1. I too am deeply drawn to Marks ST vids and methodology however his rigs are about as far detached from my little tank as almost could be the case - RO, he has plants but not many and almost always Sußwassertang or mosses, predominantly but not exclusively Caradina rather than Neocaradina, sponge filters on Aquel Pat Mini powerheads, cull tank etc. Rightly or wrongly I decided that I would do bigger water changes, like 40-50% as at this point in my knowledge and experience I see the sense in refreshing water in such a small closed system to replicate the mineral refreshment of nature to some extent. I was worried they would not react well but made sure to use water that was within 0.2 c of the water I was taking out. Sometimes it sits for a bit, sometimes not, always dechlorinator , in this case API Tap Water Conditioner. I think they’re fine and I can’t observe any adverse behaviour in any given subsequent 24h period having changed only this single parameter at a given point. I‘m increasingly of the belief they’re pretty tough little things and some of the turbidity I generate in weekly tank cleaning must push a lot of stuff through their little systems. I’ve even once or twice done a further 30% water change within an hour of the first if I think I need to. Marks’ Caradina I would suggest are far more demanding.
2. I also dose Bacter AE the way Mark suggests. Really to offer the babies something extra that’s mobile.19ltr tank. I just measured it out - equivalent volume of ten grains of Tropica soil powder i.e. the small grained version or half what I think looks like a rice grain. Half filled API test tube from kit in tank water, shaken, poured in return flow of filter pump, which remains on (although I see the logic of not doing so). Daily. The critters show little interest in other food sources I offer so I’m guessing they’re not starving. If I thought it was an issue though or there was a crisis and I was looking to alter a parameter I would cut that down or ditch it without fear. Wait a week, offer some of that nettle mix you have (guessing it’s MST stuff or similar)in a glass dish (so that the spread is contained and can be removed, syphoned out) and see if they’re interested. If not and doing their usual thing of nipping away at surfaces then the Bacter seems unnecessary. Mark himself warns of many people running into issues with it. Not sure if this is significant but the only time I’ve had a bunch of babies die on me was a day that I forgot to remove the glass dish rather than whip it out after 2-3 hrs and I was trying a brand and variety of snack food I had not before (and purely out of suspicion ) I never will again. Could be the leaving it down or the snack....or because the sun shines in the east. We can only be guided by as near to a systematic approach as possible and hope we’re not an outlier.
I really hope you get a handle on what’s going on and get a thriving community going. I totally get how you would be reticent about repeating this as I would be too. You are doing your best though and have the input of a group of very knowledgable people above. Good luck.
