I had that happen a couple of months ago on a 20 gallon newer set-up as well. What i did was:
1) Check CO2 and adjust if necessary
2) 50% water change
3) Dosed Excel at the recommended initial dose (5ml / 10 gallons)
4) Fertilize normally
5) Normal Photoperiod
Next six days
1) Dosed Excel at 2X the recommended 'Daily' dose (2X 5ml / 50 gallons)
2) Fertilize normally
3) Normal Photoperiod
1) 50% water change
2) purchased a Siamese Algae Eater (SAE / Crossocheilus oblongus) to eat the dead/weakened BBA tufts
Repeat as needed except 1 SAE per 20 gal should be enough.
My experience has been that BBA can be killed or weakened by Excel (glutaraldehyde) but unless I add an SAE to clean up the dead / weakened tufts of BBA it comes back quickly. My SAE's seem to be able to keep the young BBA from appearing but are unable or unwilling to go after mature, healthy tufts of BBA.
Today, no sign of BBA in the tank.
Last edited by Seattle_Aquarist; 08-28-2012 at 04:49 PM.
Reason: add'l info