Hi hop2jr: You have done a good job with your tank. Hope the Wet/Dry will likely improve your tank a lot,
I believe you have some medium-high light plants in there. Your lighting may be insufficient for them to grow well.
Also, a
UV Sterilizer should help you out. It works pretty well for
algae control in my 145gal tank, although my algae problem was with a white-clear one that attaches to the interior walls and decor. Make sure you get the UV tube in the wattage range you need (tank volume dependent), adjustable low-flow
powerhead (depends on the UV lamp wattage and tank volume), a flow meter valve, and make the right calculations. Then adjust by trial and error. It took me 3 to 4 weeks to clear my tank.
As for CO2, I have a few suggetions. You need to use at least three 2L bottles for a 75gal tank (I use 3 on my 45gal tank + 10gal Wet/Dry
sump system). Make sure you replace them alternatively so your CO2 injection remains stable.
Remember to sterilize the 2L bottles, and the gas separator. Also attach the gas separator to one of the 2L bottles so the height of the cap is at same level. Take your time to correct gas leakage. Consider a CO2 monitor (drop check), I built a modified DIY version, takes some time but is worth the try (Error of Measurement could be up to 36% but that's OK for planted tanks).
Pepe
Santo Domingo