This is what I use to dose nitrates. Very cheap and effective.
Shop Potassium Nitrate (KNO3) Aquarium Fertilizer (1lb Bag) for fertilizing your aquarium plants. Brand: Green Leaf Aquariums (GLA). Orders ship fast worldwide and get free shipping on orders $125.
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How many fish do you have in your 75 gallon? Have you tried adding more fish and feeding more to boost nutrients? Also, I would worry about the microscope. Everyone’s tank has Dino. The difference is whether the conditions are ideal for the Dino to thrive. For that matter, your corals produce about 95%+ of their energy via a symbiotic relationship with an internal dinoflagellate algae.