The phdown sold for aquariums is not made for plants. I made the same mistake before I was told not to use it. If there is a hydro shop in your area, they will have it. If not, there are many places online to order it and it is no more expensive that the aquarium stuff. I am also on a very tight budget so if I kill my plants, the investment for lights, fans, electricity are all for naught... not to mention not having any meds.

I had to make a two hour round trip to acquire the right stuff. But, in light of the potential consequences, I felt it was a good investment in time and effort. Best of luck!