Try not to lean on the flake food as much. And with those frozen shrimp, rinse the cube w/fresh water since I understand that frozen water they're in is loaded with phosphates. I rinse mine, then soak it it Garlic Guard and Zoe. Your fish will re-discover their feeding enthusiasm again. Try frozen vegatable matter to mix with the shrimp. No need to rinse the veggies, just mysis, brine, etc.
"Life may not be the party we hoped for but while we are here we might as well dance!"