Seachem sells nitrogen, potassium, and phosphorus in separate bottles. I was using Comprehensive but in truth, Comp is basically a trace fert. It's got a little bit of just about everything. While it's great that it's providing a variety, it doesn't supply adequate amounts of macros(NPK). Dose your macros, maybe iron from the yellowing; increase your lighting schedule and you should be good to go. Your algae issues maybe coming from running the diy co2, and then stopping it, the imbalance can trigger algae blooms.
Edit: feeding fish twice a day seems like overkill to me. Granted i keep small fish in smaller tanks than that, but i feed once a day and skip a day sometimes too.