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MPK solution without phosphates?

Gilles

Member
Joined
29 Mar 2011
Messages
116
I have this wierd problem. I bought 2 different bags of monopotassium phosphate and made a pretty strong solution with it. (>10gr on 100ml water)
Both solutions don't measure any phosphates in it using both my PO4 profi test (drop test) and also not with my Hannah PO4 tester (digital).

What i've bought:
Bag 1:
1672403791264.png


Bag 2:
1672403802518.png


1672403813376.png


What i've tested:
First off all i've tested the solution i made; which reads 0.03ppm using the digital test from Hannah.

Then i tested my tank water, which reads 3ppm on the PO4 Profi test and 2.5ppm on the Hannah test (of which 2.5 is the max output)

Then i thought; if i add part of my solution to the aquarium water (e.g. 50/50 aquarium water and (strong) solution) it should read even higher values if the solution would contain any phosphates at all; or if it did not contain phosphates it would half the values. Wierd thing was, when doing this test, the PO4 profi test dropped to 0.2ppm and the digital one to 0.15ppm.

So.. what the hell is going on? Is the stuff i bought the wrong stuff or is it somehow buffering and needs to break down in the tank before it is 'measurable' ?

1672403534300.png
 
Hi both bags look ok to me, if they are 25kg unopened they are unlikely to be contaminated or substituted.
I dont know what the test kits are measuring but I suspect your stock solution at 10% is way above the range of either kit.
Have you tried just adding the calculated dose to your tank? Or take a litre of tank water and add 1 drop of the concentrated MKP if you want to be cautious.
Cheers
John
 
Hi all,
Both solutions don't measure any phosphates in it using both my PO4 profi test (drop test) and also not with my Hannah PO4 tester (digital).
You need to serially dilute your 10g in 100ml solution by, at least, a ~thousand times to get down to a range of PO4--- ions where the tests will work.
@jolt100 has beaten me to it.

cheers Darrel
 
Hi all,

You need to serially dilute your 10g in 100ml solution by, at least, a ~thousand times to get down to a range of PO4--- ions where the tests will work.
@jolt100 has beaten me to it.

cheers Darrel
and i thought by having the solution super strong it would immediately turn dark blue...
 
Hi all,
and i thought by having the solution super strong it would immediately turn dark blue...
Yes it would, but it depends on the reagents used. Normally you would get a instant dark blue solution, and I'd guess at some point as you diluted the solution that would happen if you had more concentration of reagent.

In this case it just tells you that you are at the top of the range that the kit is calibrated for, it doesn't tell you of it is that value (probably something like 5 ppm, it will say on the kit what the range is), ten times that value or a thousand times etc.

You can think about like <"pouring water into a pint pot">*, if you pour in less than a pint it will tell you how much you've added, but if you pour in more than a pint it will only read a maximum of a pint, even if you've poured "in" a thousand gallons.

* I know a litre beaker and litre of water would make much more sense

Cheers Darrel
 
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