well for about 2 years, fert is fert it is just a matter of the numbers, I use the cheapy 99 cent ones I heard the ones for palms and whatever is a bit better, and safe because you are using them in your house for houseplants with kids and pets around them plus I have heard of others using them..I only once turned my water greenish for a few days because I used like way too many lol but it only lasted for like 4 days