i dont understand testing runoff ppm

[dank4life]

i dont get how it works. i know theres some correlation between runoff ppm and res ppm. but which way does the osmosis go? im reading 1250 at the res but 1330 runoff. is that bad?

dank4life Reviewed by dank4life on 04-09-2007. i dont understand testing runoff ppm i dont get how it works. i know theres some correlation between runoff ppm and res ppm. but which way does the osmosis go? im reading 1250 at the res but 1330 runoff. is that bad? Rating: 5

[postmandave]

What kinda system you using dank

[dank4life]

im growing in 50/50 hydroton/crutons. in 3gal bags. ebb&flow

[postmandave]

may be a salt build up .posted on ur other thread a suggestoin.

[rhizome]

to the leachate from a drip to waste system.

I assume that you're measuring nute ppm @ the return/overflow line to your res?

Evaporation of the water in nute will concentrate the salts remaining in the water.

Suggests that your plants are transpiring more water than they are absorbing nutrient salts, though evap of solution remaining in tray will also concentrate salts.

If your swing is very high, you might want to irrigate more frequently.

It would be helpful if you could describe your measurement technique in more detail.
For instance, if you are measuring the first few drops of return, I would expect a higher concentration. In this case, if average res EC was relatively constant, it wouldn't concern me much.
It would also be interesting to know the relative temperatures of res and return flow, as not all meters will compensate for conductivity/temperature.

I've always found salt concentration to be a problem in E&F systems based on a rockwool substrate- the hydroton used alone is much more stable. If you're going to use RW at all, it's best to completely submerge it each flood cycle, to avois salt buildup on RW surfaces which wick up solution but are never fully rinsed.

[dank4life]

[quote=rhizome] if you are measuring the first few drops of return, I would expect a higher concentration. In this case, if average res EC was relatively constant, it wouldn't concern me much.

QUOTE]

this is definitely the case. tyvm rhiz. tonight i'll try another method to see if its still off.