Nice to read you’re at it again.
AFAIK, people been adding MarinePure? Blocks/spheres
I'm a big fannof MarineaPure. If you're sump space allows, the 8x8x4 blocks are great! They are thick enough to have an effective anaerobic zone to denitrify... unless you hate the idea of less water change.
I would start with a single block. I have 2 in one of my system (cuz i needed a skimmer stand using one of them... hah!) and my nitrates are 0 so i wind up having to dose nitrates.
The marine pure balls work as well but probably doesn't do much on denitrification. I use both on my tanks.
If you read online, ppl will say that marinepure can leach aluminum. But, reports are inconsistent...2 test from the same tank via Triton can give a positive then a negative. But that said, I've never noticed any negative impacts to my system after all these years.