Most plant supplements should say on the bottle how much and how frequently to dose the tank.
If it does not, I would do it about once a week, after a
water change. That's what I do with my supplement. I used to use Interpet's 'Flora boost' but have recently changed and tried a couple of brands to see which works best- and I also have little tablets that I plant right beside plant roots. I found with most if not all brands it recomends once a week (or with substantial water changes)
Check that your plant supplement is
nitrate free (as you don't really want to be adding nitrates to your tank.) Also if you buy a decent supplement, it will state on it that it will not result in algae bloom if used propertly. Check the instructions and post back.
Do you know the brand you bought?
If you are unsure just try the main brands, Interpet "Flora Boost",
API "Leaf Zone" Nutrafin "Plant Gro" - see what works, but I find that they are all pretty effective if used regularly.
