2.5 issues

[Morpheus77]

So started a 2.5 gallon nano back Jan 2021. Currently have about a 1 lb of LR, and about one inch of LS. Tank did pretty good for the first 5-6 months, added a GSP, and some other type of soft coral, have no idea what it is, sorta forgot. Went through a divorce, and the tank wasn't kept up with like it should, had other priorities at the time. Anyway, I would do WC's but not enough, and I hardly ever checked parameters, maybe salinity. It went through a bit of cyno earlier this year, however I brought down the whites, and it started dying off, but my sand bed still had that decayed layer on top. The other day I checked params and ammonia was .25, and nitrates were 160. So I did about a 90% WC yesterday, and still getting 25 on ammonia this morning and 40 on nitrates. Did another 6 cup WC earlier, but haven't checked parameters yet, want to do another 6 cup change tomorrow and check then. I am running a 30 watt Nicrew LED setup, mostly run blues, with the whites on the lowest setting, and running a small power head for water movement, I have it facing mostly up. I did pull some of the old sand out yesterday and replace it with new sand. So question is, could it be I don't have enough LR maybe? I did install a small 3 gallon HOB filter yesterday, and running activated carbon, not really big enough to squeeze a sponge or purigen in there, so what are yall's thoughts on the ammonia and high nitrates? More WC's? Maybe a bigger HOB filter and run chemical and biological filtration to help clean it up temporarily? I have had success with bigger reefs in the past, but got out of it for about 10 years. I appreciate any input.