DT's is live phyto plankton. Personally I believe it is way over priced since you can grow your own in a closet for vitually nothing. I have not been able to get mine set up yet...so I am still using the store bought stuff. Anyway..its intended to feed filter feeders and such. Some swear by it...some say that it makes no difference at all. I like it and am setting up a drip system for mine so that it will be in the water all the time.