Yeah, it sounds like you were putting in WAY too much co2. Unless you have an absolute jungle in your 10 gal. CO2 dissolves in water fairly quick. I just hooked up a single 2 liter bottle to my 55 gal 2 days ago and it is sufficient. I only have about 10 plants at the moment, it raised the co2 like 10ppm and lowered my ph by .4 within 12 hrs. I've been watching the fish closely, they seem just fine surprisingly. But I can't imagine how fast the co2 would climb if I took 45 gallons of water out and doubled the co2.
Also, the quickest way to check co2 is to compare your KH and PH using the chart on this site. Click on "calculators" at the top.
Depending on the amount of plants you have, I would just go with a single 1 liter bottle for now, maybe gradually increase bottle sizes over time.