Turn Lights Off for A few Days, Do Water Tests...Figure water change volume due to nitrates and Phosphate levels, heavy phosphate and carbon the tank after Algae and Gravel Vacuum tank...
Get Rid of Nitrates, don't necessarily change all the water..of back to back 50% changes, not cleaning Filter til next day!
He mentioned he's already been doing a lot of what you suggested, and he's already blacked out the system with no results, which is why this is more confusing.