I am new transplant to this forum, and I have been posting on reef central for about 8-10 months now.
I believe in plenums, but you have to be careful, because over time I think that they can really work against you if you are not careful. Like all active filters over time they need to be rejuvenated or cleaned, and that is hard to do with all your beautiful corals sitting on top.
I had a plenum for 12 months. I fed my tank calcium acetate via vinegar in the top-off water which was fed into the limewater reactor. It worked great, Calcium and Alkalinity were never a problem, and neither were phosphates or nitrates. I feed my tank about 1 cup of 5% vinegar every 4-5 days depending on evaporation rates.
When I moved about a month ago; the tank was dismantled and I had homemade aragonite, nice big long sheets. I was kind of cool actually, but it told me that the plenum was on its way out, and the phosphates and nitrates spiked.
This time around I went with a shallow sand bed in the tank, and a RDSB (Remote deep sand bed) with a plenum/under-gravel filter outside the tank in a 5 gallon bucket. It is feed with a steady trickle of water from the main pump, and the vinegar in the top off water feeds enters the tank at the bottom of the RDSB, so it gets the nutrients first. The flow through the bucket is about a 2 times per day turnover. I just started it about a week ago, and will probably take about 3-5 more weeks till I see any results. So far pH is not a problem, but if it becomes one then I will switch to vodka.
My theory is that the RDSB will trap and or react most of my nutrients. When it starts to harden and become less effective, then I just change it out.