LR- hard to say, all times re-aquascaping. I would say, not less than 1Lb/gal. Filtration - the smallest sump with 50 micron sock, changed daily, carbon and Phosguard, plus 5g refugium (tank is 20g L) with LR rubble and macroalgae - a lot of it. Skimmer (ASM mini) is already ordered, waiting for arrival. Always can add more bio-media into the sump, if ammonia will ever appears.
What is bothering me - this sand fountain started after I disrupted system for a cleaning pre-filter. Day before it - all was normal. May be I slightly lifted plates in the corner, and now sand prevents return them being tightly on the bottom.
I know about using UGF for saltwater tanks, this was the last try to find manageable solution for a debris, collecting under the rock.
The first tank was with 2" of aragonite - eventually collected a lot of debris. Then was babre-bottom version - again, debris under the rock. To clean, have to move rock, what is unacceptable.
More flow is not an option (already 15x tank volume), LPS (scolymia, cynarina, candycane) don't like it.
I thought about possibility to blow debris up periodically, and get them collected by micron sock and Quick Filter attachment, which collects particles up to 1 mk.
Ammonia and nitrites are always 0, so I assume that there should be enough substrate for bacteria. Tank is with high bioload (filter feeders, brains and mandarin), aragonite 1/2- 3/4", for the sand-sifting cucumber, which can't keep all the area clean.