Are you doing weekly water changes? Most folks on this board prescribe to the "EI" method (it stands for "estimative index", do a search, you'll probably get links to Tom Barr's site, and is used for "hi tech" tanks that use pressurized CO2 and weekly water changes and daily MACRO fertilizers).
You look like you are doing a mix of med/high-light and low-tech tank. Ie, 3wpg which is a little high for a low tech tank, and no pressurized Co2. Its fine to do low-tech (no pressurized co2, no weekly water changes), I have a low tech and a hi tech tank (see sigs)
It does not look like you are doing any macro fertilizers (phosphate, nitrites, potassium, etc). Most folks here do 3x/week macro dry fertilizers, and then change the water 50% weekly to prevent excess fertilizer build-up (EI). Most folks here just do 50% water changes weekly and don't bother measuring kh/gh/no3/etc etc as most people have CHEAP & UNRELIABLE test kits. That's the jist of the EI method, test kits are cheap and unreliable, so why bother, we just prevent excess nutrient build up w/ weekly water changes on our high tech tanks...however, you can't do weekly water changes on a low-tech tank w/o causing CO2 instability and causing algae problems!
You need to probably add in a pinch of MACRO fertilizers (dry ferts they are called if you want to do a search, you can get them from REX for pretty cheap, and you will probably just do a pinch of dry ferts once per week same as you are doing Micro ferts once per week) Its quite possible that you have a No3 deficiency, or Po4 etc. So adding macro ferts a SMALL amount weekly would be good. Its good you are using TMG which has Ca and Mg which you need, especially if you have high water (ex: my tap water comes from a limestone aquifer, which is VERY high, like 9gh and 15kh...but, apparently this is mostly from Ca, not Mg, which you wouldn't of thought of normally)
You are doing low-tech, ie, no pressurized Co2. Your lights are a little high for this but, if you aren't having algae problems then so be it....Weekly water changes is the WORST thing you could do for your tank! Low tech tanks should get water changes every few months, or year.
You should come to realize that low-tech tanks *DO* grow plants slower than tanks with pressurized Co2. This is a "value" that some people like, I personally like not
having to weed out plants every week on my low tech tank. Perhaps you can just look at the "swap-n-shop" area here on the board and keep your eye out for some larger plants, so you don't have to wait months for yours to grow up. Be patient w/ low-tech, or if you can't be patient add some other bigger plants already (like someone w/ some needle java fern that's huge already)
Remember, plant growth is dependent on what is *LIMITING* their growth. Here you are limiting growth with 2 factors: 1) low CO2 2) No Macro ferts (your lighting is fine, and you are adding "MICRO" fertilizers, so those we are assuming are not limiting growth. The Excel does add "some" Co2, but it is nowhere near what a pressurized Co2 system would deliver, so we can assume that this is limiting plant growth as well, Co2 being one of the most important elements in plants photosynthesis process)
Just realize that you have basically a low-tech setup, and don't take advice here from folks pushing "hi tech" answers on you. You should go spend a bunch of time reading thru the LOW TECH sub-forum on this board.
Here, I'll post two very relevant threads for you:
Also, you might want to choose plants that are low-tech friendly
and there are other threads for like "Low tech Carpet" that you can search for.
Or of course your other option is to buy a pressurized CO2 system, and do the EI method of adding macro ferts and weekly WC's.
I edited this...might want to re-read if you were reading at same time of edit...