Finally... a question on home hydroponics!!

An inquiring mind asked:

"I would like to ask you a few questions about hydroponics. I live close to Phoenix, Arizona in the USA and have started a very small hydroponics system on my westfacing window sill.The 1st system is growing basil, chives, and catnip (all 3 catnip plants have died). The 2nd has tomato and stem-type onion. The house stays at 77F/25C. I use READYGRO SUPER PLUGS surrounded in Hydroton. TheReadyGro says it is made of "tree bark and organicingredients". I test the nute strength w/ a ppm meter. The ppm meter shows an INCREASE in nute strength themore it is used without me adding more nutes.I have tested 1 cup distilled water then tested thesame water 30 seconds later with 20 hydroton pieces init and the meter read a 2.5x increase in ppm, 10 to 25.
1)Because the readygro are organic, is it true theywill degrade and increase the ppm?
2)Why would the hydroton increase the ppm as whathappened in the simple distilled water test I performed?
3)What is the EC and pH and temp requirements forcatnip?
4) Does 1EC=500ppm?"

I answered:
"I asked around and found that in general, the requirements for catnip nute solution are 1.9 to 2.1 mS/cm with a pH range between 6.0 and 6.5 (and yes, 1 EC = 1.0 mS/cm). Also, just in case you were wondering, I find that an EC of 4.5 (to start, can increase this to 5.5 after acclimatation) and a pH of 4.5 (throughout) is good for hydroponic tomato nute solution.

I think what happened with your ddH2O (distilled deionized water - I assume it's deionized because of the effects you describe) is that the clay particles probably add ions to the water. This effect is most prevalent with deionized water! Try the same test using regular tap water and see if you obtain the same results. Although Hydrotron is supposed to be "neutral", it's still clay - a medium that's known to attract ions in soil solutions and release them under certain conditions. Another thing you might want to try is rinsing the pellets under running tap water (or, alternately, soaking them in distilled water) prior to your test, and definitely prior to using them, as there may be some chemical residue (for example, flame retardant) on the pellets.

READYGRO SUPER PLUGS are indeed organic, and can degrade under normal conditions. However, there are probably a lot of other factors that contribute to the changes in ppm and pH that you're experiencing, including uptake of nutes by your plants, release of root mucilage and plant byproducts into the nute solution, and increase in microbial organisms in the solution and rooting matrix. This is why it's important to monitor the pH constantly, as it's your key to ensuring the proper amount of nutes are available to the plants, and is also an effective method to prevent the growth of detrimental microbes. I would continue to add more nutes to the solution on the schedule you have, then simply adjust the pH up/down depending on the reading (the degradation byproducts from READYGRO SUPER PLUGS may not provide essential nutrients to the plants). The pH adjustment should bring everything to the levels required by the plants. "