Do a 50% water change and dose the tank with 5ml excel for every 10 gallons of water you replace, this is just the normal start off dosage as per the instructions on the bottle, you then dose normally 1ml per 10 gallons of tankwater so for a 30 gallon tank you would normally dose 3ml excel per day, but we want to overdose so you multiply 3x3ml = 9ml excel daily, that would be the normal 3x OD, as Sam says start off by 1x and build it up to 3x, and then dose 3x for the duration of the treatment, which normally is 14 days. You do everything else as normal, ferts etc, and keep the CO2 running, you will also do the normal 50% water change if running EI on the tank, and just dose the excel back @5ml per each 10 gallons of water changed. If the fish show signs of stress, stop the treatment, they will usually show signs of stress by gasping at the surface.
Certain plants may also be damaged, just be aware of this, particularily Egeria and Vallis type species, not much you can do here im afraid except remove them to another tank if you have one.
The bba will go a reddish colour, this is a sign it is dying off, for some tanks this can happen really quickly, within a couple of days, for other tanks it can take 7-10 days for this to happen, the reddish colour can be very intense or it can be very weak, when i tried it, it was very weak, each tank and treatment is different, after it has gone red(ish) it will usually go a grey whitish colour, this usually indicates the algae is dead, you should manually remove as much as you can, if you dont correct what caused the outbreak in the first place it will come back.
