Images on TPT: I gave up on TPT's image handling. I upload pictures to imgur.com first and then embed links to them in my TPT posts.
, I keep coming back to your thread because your tank made me consider keeping Blood Parrots again. Therefore, I am going through a similar thought process, weighting cons and pros and looking for an approach.
My original comments still stand and I'll try not to repeat myself.
: you will drive yourself crazy while fighting chemistry. Try to think through what will happen when you add injected co2 in your situation. Phosphate buffer + corral + pH controller + co2. Worth reading: https://en.wikipedia.org/wiki/Carbonic_acid
. The end result is constant, if slight, fluctuations in kH, pH, and co2 concentration. The more you inject, the bigger the amplitude of fluctuations. Exactly the opposite of what you aim for - stability. Moreover, co2 is not a magic bullet against algae. Algae likes co2 as much as the plants and I will bet you a box of plants that, in your situation, the algae will be the primary beneficiary. The air bubblers at the back of your tank will also work against effective co2 supplementation.
: aka CO2 booster aka glut aka Metricide and the rest, a) not effective algaecide at maintenance dosage b) effectively kills algae while damaging plants at effective treatment dosage c) slight, if hard to quantify, improvement in growth of some plant spicies when co2 is at low levels ( ~ < 5 ppm).
: again IMHO, spend $50 and get a) 2 bunches of Ambulia b) 2 -3 Azelot / Osiris//Mellon / Amazon swords (in the order of leaf durability) c) a dozen Jungle Vals d) Red Lotus Tiger. Dump them into the tank. The swords and, likely, Vals will go through transition, dumping nutrients - increase your water changes. The parrots will move the plants where they like them - and those will be the only places where the plants might survive. With just these plants + Java Fern + Anubis you can have a fully planted, fully scapped, vibrantly green and red tank. Heck, I have fully planted tanks with less species.
But you are not done yet. You cannot leave rosette plants (like swords, vals, crypts) in containers and expect them to grow normally in the long term. They need to be freely planted and for that you would need a lot more substrate then you have now. And that leads to a vicious circle: more substrate means more debris traps, resulting in more maintenance to keep the water lean. Stem plants (like Ambulia) will do just fine held down with plant weights. Ambulia grows ~ 6" per week in low light condition, worst case you replant every couple of weeks to keep the tank green. Almost anything you add to the tank means more maintenance then what you are doing now.
I am as eager as you are to find other solutions to the large fish vs diverse plants co-existence. The above is the best I can personally do.
I have posted these pictures of my low light, no co2, lean fertilizer tanks before. Hoipefully, they will give you some ideas what is doable with just a few plants species chosen carefully.
Java Fern, Ambulia and floaters only:
Blood Parrots, bare bottom tank:
I am crazy as I am considering the same headache again:
Different times: gentler fish, different water, but still no co2: