Im trying a concentrated Tomato fertilizer on my 900 gallon pond and results so far are looking good. Within a week of starting the water has completely cleared and new growth is already apprent. Baskets in the pond are Variegated Japanese rush, Marsh Marigold, Nymphaea Perry's Baby Red lily and Elodea canadensis. Im dosing 25ml of fertilizer to a 5lt watering can once a week. Ill keep you all posted though the summer to let you know how it goes.