I've got a 120 with a 100 gal Rubbermaid sump and 60 gal (former) refugium. System is about 8 years old. Had a 5" aragonite sandbed from the beginning, but then about 2 years ago started having problems with my sps color, then began to lose colonies. Sandbed looked pretty dirty so I decided to remove based on all the talk of loading of the bed after 5 years or so. Pulled out big chunks of cemented sand (had to chip off the rock), more than half had solidified. Saw no improvement in coral growth a few months after that so decided to try vodka dosing. Followed the plan at first, but then got impatient and increased doses faster than recommendations. SPS started looking better, but got cyano, upped my GFO (I had been running off and on) - this made things worse and then I lost even more color/colonies and frags. Switched salt (grasping at straws), pulled back on the vodka and finally stopped vodka altogether.
Decided to try biopellets, orderd a few liters from BRS and put them in a TLF 550 (the bigger one) reactor with the NPX screens and an MJ1200 feed pump. Positioned the outlet of the BP reactor to the inlet of my rather large skimmer (SRO/Octopus 5000SSS) so that 100% of the effluent goes into the skimmer. Soaked a liter of pellets in tank water for a couple of days with several drops of zeobac (cultured pixie dust). Placed about 2/3's of the pellets in reactor, started pump - skimmer got a bit foamy, settled down within 10 minutes or so. Wasn't satisfied with the amount of tumble, so I lowered the reactor to be almost submerged in the sump and the tumble picked up by quite a bit, then added the rest of the pellets. Also run carbon in a TLF 150 (nearly full). Did a 20% water change (Red Sea Coral Pro, switched from DD H2O), and noticed cyano starting to pull back by the 2nd week. Now on week 7 and the cyano is gone, SPS polyps fully extended and color coming back to remaining colonies and frags.
Could have been I was running too much GFO, too much vodka (got up to about 20 ml/day - 10 ml twice daily dosing), and just generally making too many changes too quickly, throwing the system further out of balance. But I am feeling pretty good about the direction now, and have got far less gunk in the tank/sump. I've still got bryopsis growing fairly well on a rock, so I've apparently got some nutrients in the system, but no HA and no cyano, and the bubble algae is even turning light green/white. But the main thing is my SPS is looking happy again. I'm keeping an eye on the pellets to make sure they keep tumbling and that 100% of the effluent goes into the skimmer, those seem to be the major factors from what I've read. So far so good, but still too new to say mission accomplished.