if you use (Matala) (I'm thinking Grey) as a false bottom, you can just use a barrier screen and then straight to ABG substrate, correct? And is a single layer (1.5 inches) enough, or do you double up?
Confirmed - exactly this is a fine way to go. Single layer is fine - the cheapest option, and Matala is not cheap - as long as you don't let your water level get too close
to the barrier screen. But you face exactly the same need with 2 layers, 3, etc.: let it wick, and you're on the road to hell. Soggy, stinky, blech.
In my bigger vivs I go 2 layers, smaller I go one. It's just a function of the diameter of the side or rear drain hole I (feel the need to) install, how far from the glass margin I can put the hole, how much room I need to leave for the bulkhead, etc. Bigger holes, bigger bulkheads, more residual margin needed, deeper Matala or other drainage layer needed.
Lovely little viv BTW, SM.