Yep, it's called the CO2 chart.............. lol. I've heard lotsa folks say don't rely on it but I gotta tell ya, it seems to be pretty damned close to what my DC is sayin. Check your dKH and your pH using liquid test kits. Plug the numbers into the CO2 chart on this site as a sticky in water parameters (I think) and that should give you an idea. The thing to be aware of is when I had a Hagen yeast ladder set up subsidized by (2) 2L bottles:
on my 30G, my CO2 levels were hideously low but my plants grew great for a while. Specially my Rotala. Man, this stuff is like a weed (lol, it is a weed!!!!). It'll take over your tank if you let it. I never had a green water bloom, just had some green hair algae on the glass. BUT, eventually came BBA and boy when it came, IT CAME! Almost killed my Rotala and there is still evidence of it in my tank.
I was a cheap ass too and didn't think I needed to go pressurized and played mad scientist mixing wild concoctions of different yeast/water/baking soda/no baking soda/warm water/cold water/up to (6) 2L soda bottles at once..... man if it was possible, I tried it!!!! None of it saved my from the 3 HIDEOUS bouts of BBA that nearly wiped out my tank!
My experience tells me (and I'm sure I'll get reputed by others as I have b4) any tank over 15-20G, I'm gonna have pressurized CO2 on (if it's high light) cause tryin to maintain adequate CO2 levels with yeast is just like a dog chaisin his tail! I know the box says (from memory so I think this is factually) that the Hagen ladder set up is good up to like 30 or 35G. IT'S A LIE...... Don't believe it for a second. You're probably gonna say to yourself "Hm, this guy is fulla crap. I can make this thing work"..... most do. Best of luck to you and I hope that works better for you then it did for me, HONESTLY. But if you're experience is anything like mine, within the next two months, you'll be throwin that stuff in the trash and buyin a pressurized CO2 system.