on another thread davidstcldfl referenced the following concerning DO, gpm water flow in their troughs

scrol part way down the page...look for 'Flow rate'...
http://hosted.verticalresponse.com/5273 ... 51f16240b/
Sorry, I didn't seem to 'save' part 2...?

but, the part that interested me was the mentioned the level of nutrients measured at the beginning of the grow bed and after flowing through the grow bed remaining close to the same.

a couple of months ago to try and determine nitrate usuage in a system, i removed the fish and drained a 65 gal aquarium that had been supplying nutrients to a 4' x4' x6" (60gal capacity if filled) contineous flow mat grow bed. I then added water from another aquarium with a nitrate reading of about 80 with a API test kit.

the grow bed has 3 fair size producing tomato plants, 3 fully grown kale plants, about 50 narcissus and daffodil bulbs, 20 glad bulbs, some herbs, a couple of chile plants and some misc. cuttings. after two weeks the nitrate level was reading 20ppm. i realize that i did not factor for concentratin of nitrates due to evaporation, was not able to isolate and measure a growth comparrison to a similiar set up with a contineous flow of 80 ppm of nitrates. but, the plants continued to grow, flower and produce tomatoes and chiles.

however, i expected the nitrates to hit 0 in just a couple of days based on the plants 'purifing' the water. still searching for an equilibrium at what point the level of nutrients can be expected to produce a desireable quantity and quality of plants. a lot of variables i know, but there is a common denominator across the board at some point.

nor, i have i ever seen the nitrates noticeably fluctuate between morning and night. what am i missing here?