Uptake Rate and RI


Prolific Poster
Apr 4, 2005
For some reason, it seems like my plants do not uptake very much NO3 on a daily basis. The EI dosage I use is below. After a WC and reset, I test the NO3 (Salifert NO3 Kit) at 25 ppm and it only reduces by 1-2 ppm daily. My question is; should I dose fewer times per week? I'm concerned that if I dose as below 4X per week, I'll end up with NO3 at 100+ ppm by week's end. I think I understood Tom to say the approach is to to use for slow uptake is to dose the recommended dosage, just less frequently to address slow uptake.

Thanks for the help!

KNO3 = 1.25 tsp 4x per week
KH2PO4 = .25 4x per week
MGSO4 = .25 1X per week at water change

Flourish = per instructions
Flourish Iron = per instruction
Flourish Excel= per instruction

Tank: 150 gal. dosed as 130 gallons of water
Light: 4X 96 watt PC (2.56 wpg)
Photo Period: 14 hr at 2 X 96 watts and 5 hrs at 4 X 96 watts
KH = 16
Ph = 7.3
CO2 = 24 ppm

Tom Barr

Staff member
Jan 23, 2005
Re: Uptake Rate and RI

Your max uptake might be higher, this depends on a number of things.
But 2ppm a day is good.

You can back off the dosing of KNO3 if you want. No need to add more than 20-30ppm per week really.

Read the math section in the EI article.
The max amount of build up is 2x the weekly dosing if you do 50% weekly water changes and have no uptake at all by the plants.

It does not inifinitely build up which I think many wrongly assume.
You can verify this mathmatically and also through using good test kits and plotting.

Tom BArr


Prolific Poster
Apr 4, 2005
Re: Uptake Rate and RI

Thanks Tom,

Is it possible my slow uptake and slow growth could be from some other limiting factor like potassium or iron? Also, have you ever heard of high KH or sodium levels slowing down growth?

I raise my KH with aking soda and I also add African rift lake salts at WC.