It does look quite heavily planted, maybe you do have some dead spots in the water Whereabouts are the filters, spraybar, airstones, powerheads (delete as applicable!), what happens to frozen food - I can easily tell you how the water moves in my tanks as the food moves in the currents and the plants sway about. Does grot collect anywhere in particular? Might not be sulphides in gravel as such, could just be similar to FA's problem?
It's got to be heavily planted for the line-of-sight break-up. Removed a couple of pieces of bogwood during the clean-up though. The filter's an external Eheim 2213, spraybar along the middle of the back wall of the tank (Stripe is probably in front of the spraybar in the pic). The air stones are generally along the middle or the front of the tank (these need reconnecting as I got distracted during the tank build-up).
Detritus doesn't really collect specifically in one spot.
Just a quick update to let you know that Stripe is still OK today. Despite the fact that, 2 days ago, he was removed from the tank and put into the same tank but with his territory largely gone and the tank looking completely different, he's very keen to eat, and even approached my hand tonight as I went to feed him. Poor thing must be ravenous!!
Haven't seen the fry today, but I've been too busy to really look for them.