You could get a TDS (total dissolved solids) tester to see if you are starving your plants, or burning them with too much nutrients. Also, check your pH and make sure it's in the right range, maybe 6.5? Lastly, are the roots getting wet? I know that seems simple but it's another thing to check. Good luck.

Hi Rrothrock,

I doubt if you are starving your plants, but it is quite likely that you are burning them with too much nutrient as Klein above suggests. When the pH is severely out of range, you might be burning them, but if the pH is out of the range of 6.4 plus or minus about 0.3, your plants will generally stop active growth as they are unable to obtain soluble Iron.

To see an explanation for this, please see my Australian web site below.

If you save each page as its own name, on to your computer, all in the one directory, then you will be able to navigate from page to page when you are off-line.

Go to the page "Plant Foods" and see what it says about Iron in the "Minor Elements".
Then go 3/4 of the way down the "FAQ" page and look at "What is the Importance of Iron in Plant Growth?"

Cheers,
Jimr007
Australia.

Here is a link that might be useful: Simple Sand Hydroponics

Why do you suspect it is lack of oxygen? Are you using an air stone? Also, what was the transfer from  water to nutrient solution, soil based to water, or soil to nutrient solution? Were any roots damaged in the transfer?