Many ways to add PO4 to a tank
Kh2po4
k2hpo4
nah2po4
Flourish phospherous
Kent botanica phos+
Fleet enema (yes this is correct)
KH2PO4 is the most common other than the Commercial ones and fleet enema.
http://www.gregwatson.com sell it and 1 lb will last you over a year easy. Cheaper this way but some perople perfer to just buy commercial and save the hassle of mixing it up.
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