Can you explain this a little more please?
Not sure how much You know at this point, so here's the basic run down:
Lighting Rule of Thumb: Xw/g=Low, medium or high light. This rule applies generally to tanks from 10g to about 125g--then, in either direction, it begins to break down. For tanks in that range: 1wpg generally does not work. 2wpg works and puts things in a Low-light range. 3wpg puts things in a Medium-light range. 4wpg puts things in a High-light range. 5wpg put things in a Very High-light range. More WPG=More C02, More Ferts, More Work, hassle and expense.
Below 10g (nano) there is a need for More WPG in order to achieve the same effect, and above ~125g there is a need for LESS
to achieve that same effect. Not sure why it works that way--but that's the way it is.
So, having such a large tank requires less WPG to achieve whatever level You seek. Having 6wpg put You in the Very High-Light range--even on a tank in the 10-125g range. On a tank the size of Your's--You are in a Super-Duper High-Light range. The plants are being driven very hard by that much light and need probably more C02 and ferts than You can supply. Hence--Reduce the lighting--Step 1. Then You will put Yourself in a position to actually be able to supply enough C02 and ferts. You are having Problems because everything is "Out-of-Balance". The first and only Step toward getting things in balance is: Reduce the lighting. Without that--You're sunk. You will never get it in order.
Phosphorus/Phosphates. Ferts need to be in balance also, but that will come after
the lighting is reduced and the C02 is cranked up! Ferts are interdependent--a shortage of one will effect the ability of the plant to use the others. I.e., Insufficient P and K (potassium) will reduce the plants ability to absorb nitrates. You apparently have enough P and K to absorb all of the nitrates, but then come up short on the P also causing an imbalance resulting in the green spot algae that You see on the leaves. Because all of the N (nitrates) are being absorbed--You are seeing the slime algae. Everything is out-of-balance--Because
You have WAY
too much light.
Meat eaters...after I sell them, I plan to only have 2 small meat eating plecos in there, a gold nugget and 1 L-134.
Doesn't seem to be any issues here---just personal choices.
In my eyes that makes everything much easier/simpler--no serious need to worry of the overall TDS, Gh, etc A Planted Discus Display tank is always much more Beautiful and impressive to me and makes everything much easier without the "Breeding Parameters". I've been around SD, and DAAH, etc and I really would like to see those folks update their thought processes. Yes, they can breed discus in a bare bottom tank--beyond that--most--of them are pretty clueless. But they are die-hard in their beliefs and there are "Wolf-packs" on those forums that come out in attack mode when someone goes against their dearly held belief system. So, if You want a beautiful Planted Display Tank--stick with us. In a yr You'll be able to go to those places and see exactly what I'm talking about.....
I guess in short your advice is to lower the light and increase the CO2 somewhat. What about the KNO3, I really fear/detest green slime algae.
Not "somewhat"--Crank It Up!
Just follow the advice posted earlier so you don't gas Your fish. Its NOT
that easy to gas Your fish, but there is an invisible line in the water--so just use some caution and keep reading and do a search or 3 on C02.