OK,

so my 50% nut solution when first made reads at around 1000PPM.

but when the res gets down low, from say 6 gallons to 2 gallons, i take a reading and it shows up as 1300PPM?

is this normal? i thought that it was supposed to go down as the plants use it?

also, if i take daily readings, it would go down down down, then as its near empty, it would be high

im thinking maybe particles from the rockwool?


Last thing, what can i do about not having green fungus or whatever its called (maybe its mold) thats forming on the drainage tray?

(its a big bin that was cut down to only be 10inches tall, and during veg stage, i have a drip-like system feeding it 4 times a day, and then when they go to flowering, it gets changed to a ebb and flow setup)

As the water is used up/evaporates, the mixture that is left is more concentrated...if you added plain water (with a low ppm) back up to the 6 gallons and took a reading it would be less than 1000. The plant will be using nutrients.

As Socrates7 said, the reason the ppm is rising is because the concentration is also rising as your water evaporates. You will lose much more water to evaporation and plant consumption than you will nutrients in the solution.

so the real benefit of having a PPM is knowing when to add more water to what you already have, and also being able to easily figure out how much more you need to add to keep your nut ratio at whatever % you want it at...

makes sense now.

Evaporation and or transpiration is happenening faster than the plants taking up the nutes is all . Add back , top off the res. w/ just H2o till it's back down to 1000ppm if that was your target .
Peace
Crispi

remember the plant will use the nutrients it requires and leave what it dosent. You can only top up for so long before you will be left with too much of one thing and not enough of another, it can also lead to nutrient lock out if you get a build up of one and build up of toxic salts (faqs). I change once a week'ish. I top up once with full strength then once with 1/2 then just plain water, once ive put in the same volume as the res holds i change. Ive read various methods though..this works for me. but you need to do a full change atleast every 2 weeks..when i left for 2 weeks (topping with 1/2 strength) the plants didnt look so good!. Im new to dwc though.