meter costs just a few bucks. Jeff was right, your algae is binding the phosphates before they can register on your test. Fish need to eat, so don't starve them, you need to strike a balance for long term health.
Phosgard is a good start along with aggressive water exchanges. A protein skimmer is a must IMO
as it's the aquariums first line of defense in filtration. Live stock like crabs help, but they just recycle the nutrients and more algae grows. Removal of the algae and reducing the available organics is about all that really works. Everything else is a temporary solution.
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