Herp safe plant fertilizer

I have little planted pothos (potted) in with all my baby crested gecko grow outs. I use old water from my fish tank to water them most times but many of the plants are looking puney. Is there anything I can just buy to stick in the dirt or water them with that's safe? I'm a horrible gardener. Pothos and aquarium plants (bc u don't have to water them, ha) is about all I can keep alive.
Thanks :)

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Pothos generally don't require much nutrients, but I would imagine a low dose of worm castings wouldn't hurt anything. Also, if you don't water often and let them completely dry out, the plant can become root-bound, which means when you give them a light watering the water flows right through the soil due to compacted soil. You could just take them out and thoroughly soak them and let them drain.

Thanks so much! I didn't even know they sold those.