I discovered by accident (and not a good thing for me) that rooibos tea lowers PH. I put in 2 bags of tea in a 10 gallon tank and it lowered the PH by over .6. Not good for me since I already have low PH, but possibly good for you. Kroger carries it in their Private Selection label if you can get to a kroger. Even better, it's actually good for your betta so you can leave it in long term.