Hi, i have a 29 gallon with 2 amazon swords, a bunch of dwarf sag, wisteria, and compacta.
I have eco complete substrate
48 watt nova extreme light raised on legs
and i dose flourish exel once per week
I have a 50 dollar petco gift card and i might purchase a GLA 45g co2 system
I'd say go for CO2! Reduce your photoperiod until you get CO2 on the tank. Remember, as long as there's light on, photsynthesis will be occurring, and if you're short on CO2 compared to the length of lighting, your plants will be trying to create sugars and grow without a key ingredient.
It like trying to bake a bunch of cakes. If you have a lot of sugar, flour, butter and chocolate, but only two eggs, how many cakes can you really bake?
i would go with DIY. its pretty easy to do and a bag of sugar and some bakers yeast will set you up for quite a while for a lot less than those 45g systems cost. if you find you want more CO2 with DIY, a gang valve and another empty soda bottle can get you there, or you could just find a really big bottle and use that.