I have a 55g planted tank. Low-tech, pool filter sand as substrate.

I've never had great luck in this tank, but in early September I took the advice that having more plants often leads to better results, so I planted a good number of plants.

However, two months later the new set of plants also don't look great. The water wisteria has shown browning/yellowing and a lot of leaves melted. The valisneria has some runners coming off, but still looks lethargic and brownish. The epiphates sprout new leaves, but some of the old leaves also have a yellowish look and some even have holes. The pearl weed died immediately. I'm seeing gradually more algae.

Water parameters:

• pH: 7.6
• Ammonia / Nitrite: 0
• Nitrates: 20-40 (hard to clearly tell them apart on the API test)
• Phosphate: 5ppm
• kH: 1*
• gH: 5*

Care routine:

• I dose 1x/week with Easy Green All in One, then 2x/week with extra potassium.
• I have homemade osmocote root tabs below all the rooted plants
• Biweekly 30% water changes
• I have a 42w light on its second lowest setting (25%, according to the package) for 7 hours/day.

I understand that my CO2/nutrients/light equation is a bit out of whack, but I'm not sure what to do to fix it.

ChatGPT suggests that my nutrients are missing, but I already dose enough to keep my nitrates high. I'm more inclined to suspect that maybe I'm providing too much light, but historically when I've changed the lighting I've only made things worse.

Any advice or insight?