If you're going Down The DIY road on a 80 gal, I suggest getting a few 2 lit bottles and doing the mixing yourself, you'll need several bottles to support that size a tank.
while 1 system will improve plant growth, that's a very minimal amount of co2 for such large tank. It also depends on how much plant mass you have and since it's such low co2, reduce as much turbulence at the surface as pos, it'll minimize loss.
Do not use an airstone to diffuse co2 if nothing else use takeout chopstick, shove it into the airtube and snap off the end. With 1 bottle of co2 you won't need a drop checker or bubble counter, the amount is so small it'll never get dangerous for your fish.
I used to use 2 DIY 2 litter bottles for my 15 gal planted. I switched out ea bottle every other week. I connected them to a mini internal filter so that the bubbles r chopped into fine tiny ones smaller then my glass diffuser could produce