How Much Po4 Actually?

fitos100

New Member
May 17, 2019
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I made a fertilizer from KH2PO4, so I can add PO4 to my plants.
From the rotala butterfly, I made the calculations and I came up with 2.54 ppm of PO4 per week.
So if I put 12 ml of that solution per week I should take 2.54 ppm of PO4.
I divided to 4 ml each time I dose, so 3 times per week.
I do my PO4 liquid test and I found 0.3 ppm of PO4. I did the test, few times during the week and I have 0.3 ppm all the time.
My question is, where is the rest of PO4? my plants consume all the rest of PO4 and I left with 0.3 or is not actuall 2.54 ppm my solution from the calculations??
 

fitos100

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May 17, 2019
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My tank is 300 L
The solution is 5 gr KH2SO4 in 55 ml of distilled water. For 12 ml dose per week I get 2.54 ppm PO4.
 

T.Smith

New Member
May 25, 2019
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my PH is 6.4 and i dose one day PO4 and the next CSM+B chelated for Fe and micro elements.
Hey fitos I’m actually been having this same exact issue with dosing my KH2PO4 this week. After dosing 1.5ppm of po4 3x a week my test always show up at 0.3-0.5ppm I figured it was consumption, so I wanted to dose a little more to get to 1.5ppm a 10:1 KNO3 to po4, so I raised my dose to 15ml instead of 10ml, my ferts calculator said I would be dosing 2.25ppm that’s .75ppm more of po4 I dosed 3 times this week tested my po4 just this morning it was showing 0ppm-0.25ppm? I’m starting to think it’s my test kit, if you find anything out let me know and I will do the same thanks! My ph is also 6.4 and I dose CSM+B chelated for micros 0.3ppm every other day does this have anything to do with it?
 

fitos100

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May 17, 2019
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To get things from the start, I add one day, KH2PO4, KNO3, MgSO4, K2SO4. and the next day I add CSM+B chelated. My fertilizers calculated with rotala butterfly are:
NO3: 7.36
PO4: 2.54
K: 9.64
Mg: 3.56
S: 6.30
Fe: 0.15
I want to start and make the EI method because I agree with Tom Barr is more easy to change more water than re calculate your fertilizers doses all the time.
I make tests with JBL. except the Mg test which is difficult to read the colour, the rest are very nice.
My results are,
NO3: 20
PO4: 0.3
K: 35
Fe: 0.1
 

fitos100

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May 17, 2019
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Fist off all I do water change around 80 liter (300L tank) for the moment. As I see the results I understand the build up of NO3 is because of the plants and the fish feeding. Also the K is build up because I don't make 50% water change. What is confuses me is the PO4 and the Fe stay low.
 

T.Smith

New Member
May 25, 2019
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Mechanicsburg , PA
Fist off all I do water change around 80 liter (300L tank) for the moment. As I see the results I understand the build up of NO3 is because of the plants and the fish feeding. Also the K is build up because I don't make 50% water change. What is confuses me is the PO4 and the Fe stay low.
So your dosing .843ppm of PO4 3x a week and at the end of the week you end up with .3ppm of po4 so your plants are possibly consuming .54ppm of each dose, I wouldn’t think this is completely out of the ball park, all considering multiple unknown variables it very much could be contributed to just rapid root growth, PO4 is contributed to many key functions of photosynthesis and it could just be contributed to plant growth. My tests show an uptake of almost 1ppm in a day, but also I’m not an expert this is just from my experiences lately with dosing Po4. I feel like my tank likes and uptakes more po4 in comparison to other nutrients, but I also have a lot of new plants expanding their root masses and all of that good stuff. As far as fe goes I really can’t contribute because I don’t have a good test kit yet for fe. I hope this might help. T.Smith
 

fitos100

New Member
May 17, 2019
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I also think is the difference of the plants consumption. I will try to raise my PO4 to 3 ppm per week and check the difference.
What really confuses me is the K which although I add 9.64 ppm, I ended up with 35 ppm and sometimes more. My water change is 0 of K.
 

T.Smith

New Member
May 25, 2019
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Mechanicsburg , PA
Seems like there might be K in maybe something else you dose? I use reKHarb for kh and it adds about 10ppm of potassium each dose. Maybe the test is just showing more then is actually has? Your JBL test kit, is it the master kit with the liquid test? or is it the dip strip? I know jbl makes a test kit that uses your phone camera to read the colors and they are really inaccurate because all cameras pick up color differently.
 

fitos100

New Member
May 17, 2019
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This the reason I bought dry fertilizers so I know what I am adding. At the moment I only add K with KNO3, KH2PO4 and K2SO4. The number is 9.84 ppm. My jbl test is the proscape case the liquid one. I don't know maybe I must make I big water change to get it zero and then check it again.
 

T.Smith

New Member
May 25, 2019
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Mechanicsburg , PA
Oh awesome I’ve been eyeing that test kit up for a little while glad it’s been working alright for you. Maybe adding the Fe/micros does have an effect to the po4 but I always thought the reaction between po4 and iron you would loose the iron not the po4. I did my po4 test today, Sunday I did wc added back the po4 mid day, tested for about 2ppm right after, added micros this morning and po4 tested in the evening at .25ppm, so my test show my plants used 1.75ppm in 24hrs? Do you think this is accurate, I’m useing cheap api test kit for the time being not sure how accurate it is?
 

fitos100

New Member
May 17, 2019
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The JBL tests are good except the Mg which is difficult to reed the color. For API I don't have trust. Even their test cube if you add 5ml with syringe, is above the line. I will make some more tests with my PO4 and let you know.
 

toads74

Lifetime Member
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Jun 3, 2013
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@fitos100 have you calibrated or validated your PO4 test? Toss a day’s dose in a cup of ro water and test it. If it doesn’t go off scale it’s not detecting the inorganic form, and is only showing the organic. Had this with a nitrate test and had to switch brands. Don’t know if it was just a bad bottle, or the test design.
 

fitos100

New Member
May 17, 2019
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I did like you said. I put 1/3 of the weekly dose, 1ppm in glass with RO water. the colour in few seconds become dark blue almost black. So the test is ok?
 

fitos100

New Member
May 17, 2019
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I just tested again my PO4 before my lights are on again. Yesterday I raised my dose from 0.85 to 1 ppm per dose. So from 2.55 per week now I add 3 ppm.
I found 0.5 to 0.6 ppm. So is the 0.2 difference from my last dose. As a conclusion my plants consume 0.55 ppm per day and 3.85 ppm per week.
So should i raise my PO4 to 4 ppm?? isn't to much? ( I start to change once a week 50% of my water).