Ah, yes. Tank size; that was the variable I was missing.
It's on a 20L, so I suppose worrying about too high of a concentration is in order. But with the amount of 02 the plants are putting out, oxygen levels should be good. Is there a toxicity level in regards to CO2? I aerate significantly at night, so I'm not worried about suffocation. I've been looking locally for a hardness test kit to calculate my concentration of CO2, but they don't seem to be carried anywhere. I'll have to get a drop checker online, unless there's a DIY version of that.
Anyway, I guess I answered my previous question. With the mixture I use now, I can manage 1/2 bps per 1 gallon jug for roughly 3 weeks, sometimes four. So for a larger tank, at 5 bps, I'd need ten gallon jugs per 3 weeks. Staggered, that would mean changing a jug every two days or so, which wouldn't be ideal.