Until a ~1 year ago I used to have a similar tank (22g) going for ~ 6 years. It was one of my least problematic tanks, 99.9% algae free. The major difference that just jumped out at me was that you only have 3 species of plants that are not known for being fast growers. I am thinking that different plants consume nutrients in (slightly?) different amounts and at different rates.
That tank was relatively over-stocked: 12 black neons, 4 ottos, a beta, 4-5 black mollies, etc. And I always tend to over-feed - by a lot.
So, if you can find a faster growing plant or 2 that would fit into your scape, the 'balancing' will get better.
