Big Dog Mom

I have Matrix in a fine mesh bag in the far left compartment. I have the blue/white stuff in the other two compartments, cut to fit. I will switch up the bio media as this whole thing started because I wanted my plants to look better. My snails are fans of the coarse sponge on the HOB intake. Thank you for your advice. Most welcome.

Marina 15 HOB power filter. Space for 3 cartridges. Replaced one cartridge with a fine mesh bag of Seachem Matrix, and 2 cartridges with TopFin blue/white filter media - looks like quilt batting. When I cleaned the HOB housing today, I did it in a bucket of tank water, rinsed out the Matrix in the bag (to reduce the grossness) and replaced half of the filter media.

I have a 10 gallon, lightly planted tank with two small fish and two Nerite snails. I put 3 API root tabs in the tank because the plants seemed like they were struggling a bit. The tablets immediately dissolved on contact with the water so I could not bury them and for two days the water was milky/cloudy. The water was clear a few days later (Day 3), but the water parameters are now high. Before the addition of the root tabs water was pH 7.8, ammonia 0, nitrite 0, nitrate between 5-10, if it got to 20 I did a water change. After root tabs, pH is still 7.8, but the rest have spiked. After 5, 50% water changes, once a day, I'm still getting ammonia 0.25-0.5, nitrite 0.25-0.5 and nitrate 40-80. Using API Quick Start and Water Treatment for each water change. Today the HOB was loaded with orange/brown algae. Do I just start over? Is there something I can do to fix the water? What I'm doing isn't changing water parameters, so help please.