It's great watching these tiny creatures hunting through their small home. I finally got some
really fresh mosquito larvae, meaning they move a lot, and the glassfish are enjoying them so much, although some are almost too big for their mouths. I'm afraid I'll have to keep them away from the archers for quite some time...
The diatoms have now been reduced down to an acceptable level, essentially dirtying a bit just the substrate. The nerites have surely helped, but surely other factors have intervened. I believe the problem was not silicates in the tap water, otherwise I'd have never solved it (which I didn't, not entirely, not yet); rather, in the sand, or likely the tank was not fully cycled.