Just for future reference, you can add vinegar to a tank to drop the pH. Go slow - it doesn't take a whole lot. For my 300g system, I used around a cup at a time and waited a few minutes to check the result. When my tank crashed from my runaway kalk reactor about a year ago, I added almost a gallon to drop the pH from 10.0, and it dropped to below 8 in a matter of minutes...