I think it's GHA but unsure as it's really tuff to remove of the rocks when trying to manually remove it. Tank is 6 months old, currently Nitrates are at 10 PPM and 0.08 PPM phosphates. RODI water also at 0 TDS. Stocking I have 1 tuxedo urchin a pincushion urchin, 10 trouchus, 10-15 hermits, 10...