WO,
To be on the safe side try contacting Waterlife directly, they are very helpfull.
According to the directions I have:-
Dosage: Add One tablet for every 5 gallons (25 litres) of water on days 1,2 and 3.
Water change on day 8.
What type of filtration are you using, you may have to use only half dosage?
www.waterlife.co.uk
Regards.
Mick M.