Anyone want to assess my tank?

[Delphinus]

Here's my thought .... I bet it is PO4. Biopellets apparently can only reduce PO4 as long there is NO3 alongside. PO4 is also very difficult to test, but it does inhibit calcification which turns into recession fairly easily.

For me PO4 is a constant battle. I use a cup of high capacity gfo per week in my 280, and if I miss a week I notice immediate effects.

I suggest adding some gfo for now and see what happens. It can't hurt..