my bad, phone dead at the moment. i think 3 hours would be enough. The recommended safe dosage is about 100 mg per 300 gallons. I on the other hand didnt know and have been feeding 250 mg in my 300. i put in a 250 pill this morning. going to see how it works out for my new female marbled when i get back home. i'll text you the results. as of now i have all lights off though to keep stress down.I texted u lol