I used to maintain a fairly large culture of phyto, and experimented with different ways of dosing and the effects on the tank. I did see a benefit to animals that consume phyto, but I did notice an increase in phosphates and nitrates.
I spoke with another member about this, and he offered an interesting (though not very practical) solution. Even though it wasn't very practical, I decided to try it. I went on eBay and found a centrifuge that would suit my needs. After culturing phyto to a high concentration, I would put in the centrifuge and spin it down. I would remove the liquid left at the top, and add RODI water, then spin it again. This essentially "rinsed" the phyto of the nitrate and phosphate heavy water that they were suspended in. I noticed the same benefits to the tank, with minimal increases in nutrient levels.
Basically, the phyto itself doesn't add a lot of nutrients to the tank, but the water that it is suspended in will. If you want to dose phyto, I'd encourage you to culture your own, or buy it from someone locally. In order for the tank to really benefit from it, you'll want a high concentration of phyto in the water so that you can dose smaller amounts. You also want to make sure that the phyto is alive, otherwise you're just dosing nutrients. You don't need to buy a centrifuge, but taking the above precautions will help you avoid doing damage to the tank.
