The smaller the res the quicker and more fluctuation of PH occurs. If you can get an extra stone in each bucket, that would be great. I use 4 12" stones in my 25 gallon ebb 'n flow res as well as one more in my table that comes on when the pump comes on. Consider using Botanicare's Hydroguard in your res. I have never had any algea problems. Your PH target of 5.8 is perfect. Best of luck....