What are the factors you need to consider when balancing in your tank and what is the one factor of those in your tank thats pretty much a constant that you have very little to no control over currently?
Which ones do you have control of?
Pennywort can make good high metabolism floating vine. You can attach a fishing line lasso on edge of tank and manage it there so it doesnít shade what donít want it to shaded. When it starts to creep to many runners out under your light you simply snip out nice new growth on end, cast the bulk of old growth away and re-tie shorter fresh new part of vine back exactly where you want it. When managed properly, which only takes about 8min every 7-14days, it only casts a very light shade just exactly where you want it. And man can it process waste and exchange gases. Once those lily pad leaves break water surface and have free access to all co2 and light they want they can really process ammonia and phosphate.
A nice piece tied up to left of input of your filter over crypt bal (?) would actually be perfect, maybe another one tied up in back right corner. Your little tetra etc will actually appreciate having a little floating cover, theyíll feel safer.