Gotcha... I'll have to measure the tanks when I get home, I was guess-timating, but I think I only have about 6 in each tank, have to count as well!
This last weekend I added water with a conditioner to the tanks, I added about 3 gallons each, but the water level was about 1.5" low... so maybe I am wrong about the size... here is a pic, but it is hard to tell how big they are.