Rescued tank, need help with levels
Hi, so long story short, someone I know was going to flush their remaining fish (long tail zebra danios) after majority of them died and I offered to take them instead. They gave me a 30 gallon tank, their level testing equipment, solutions by Seachem (prime, stability, and pristine) and obv their remaining fish. Currently the ammonia levels are .25ppm, nitrite is .50ppm, & nitrate is around 20-40ppm. What do I need to do to lower the ammonia and nitrite ? Frequent testing and water changes until it fully cycles again?
I took it home (6 days ago) and was able to save around 50% of the original water. I did scrub the tank with a wet sponge (no soap) due to a bit of algae and what appeared to be mold near the top of the tank. I treated the new water, with all three solutions, before adding it to the tank, and I added a sponge filter with an oxygen pump. The levels are significantly lower now from when I received the tank, but not where it needs to be. I did a water change (around 40%) three days after getting the tank because the levels spiked to 1ppm for ammonia and nitrite. I added a few plants because I read they can help lower the nitrogen levels, I vacuumed around half of the gravel, and changed their filter and ammonia reducer for the back hanging filter. I would appreciate any advice as I am a full on beginner. My long term goal is to eventually get to a fully planted set-up, add some bottom dwellers like Cory’s or Otto’s, cherry shrimp, and substrate change to sand etc. Any advice on how to lower my ammonia and nitrite levels? Here’s a pic attached of what my tank looks like now. I will be doing another water change today around 30%. Thanks in advance!