sciencefiction
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- 26 Feb 2013
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My target NO3 concentration is 10 - 20 ppm.
Is this concentration your weekly target or daily target? As far as I know one doses every day or every other day, in order to achieve 10-20ppm total per week. Therefore at any given time, providing your continuous water changes, you want 10-20ppm divided by 7 days? A TDS or EC measure is a snapshot in time. It is the concentration there and then and it does not get any lower than that as time goes by.....
The total PPS-Pro salt equivalent of 10 ppm NO3 = 10 x 85g/20g = 42.5 ppm by wt.
What you're calculating above is not very clear to me. You have:
20g NO3 in 500ml distilled water solution.
You want to achieve 10-20ppm concentration in the tank itself. I will assume you want that measure constant every day, not a cumulative effect....? Either way, for the purposes of calculation I assumed you want that daily....though that's to be disputed...
10ppm = 10 mg/l
If tank is 130 litres, then to achieve 10ppm NO3, you'll need 10*130/130 mg/l = 1300 mg/l = 1.3 g NO3 for your 130 litre tank.
In the given scenario you have 20g NO3 in a 500 ml solution, so you roughly need to dose 500/(20/1.3) ml to achieve 10ppm NO3, which is about 32.5 ml dose from the solution. If you spread that amount over the course of 7 days, it is 4.6 ml a day.
Do you dose 32.5 ml daily or do you dose 4.6 ml daily, or thereabouts?
The total PPS-Pro salt equivalent of 10 ppm NO3 = 10 x 85g/20g = 42.5 ppm by wt. The corresponding EC rise = 42.5/0.64 = 66.4 uS.
10 - 20 ppm NO3 = 42.5 - 85 ppm TDS
Corresponding EC rise = 66 - 133 uS
I am not sure how you arrive at the above figures? In my view:
10 ppm NO3 @ 25C is 10/0.64= 15.64 EC
20 ppm NO3 is 20/0.64 = 31. 25 EC
OK, my tap water reads 346 uS and my tank is 442. What does that say about my water?
Let's say 20ppm NO3 is your daily max amount you want to allow for in your TDS/EC reading and you have an increase from 346 to 442= 96 EC, which by the way is an increase in EC(TDS) of 27.75% !
.
For the purposes of better understanding I will use both EC and TDS values...
96 EC is the equivalent of roughly 61.44 ppm, from which at values for
20ppm NO3 - only 31.25 EC from the 96 EC rise
10ppm NO3 - only 15.64 EC from the 96 EC rise
I am pretty certain PPS-Pro recommends the 10-20ppm as the weekly measure and not daily, therefore if you are to achieve max 20ppm NO3 per week, your daily differential from base tap water to account for the daily NO3 dose, assuming plants used none of it at all, is 31.25 EC/7 days=4.46 EC on top of your base water, or your EC reading should read 346+4.46=350.46.
Which means you have 96-4.46=91.54 EC unaccounted for in you daily EC test, give and take the other ferts and plant uptake...
NO3 is the fert at highest concentration...So again, I think you're either severely overdosing or there's more than just in-organic fertiliser buildup in your tank....