Re: Thought I knew about algae... I was wrong
Ah. Yup, it definitely has something to do with it. It is essentially a new tank given the new substrate and lighting, so it hasn't reached a balance yet. I suspect your ammonia levels are a bit high-is it brand new aquasoil? If you had a large external filter with plenty of microbial growth this wouldn't be as much of an issue, but that's a small tank for sure.
I would recommend large-ish water changes for the next two weeks-keep the lighting as is and make sure your co2 is maximized. I have a hunch you're experiencing a new tank syndrome of sorts.