peet Posted May 29, 2014 Report Share Posted May 29, 2014 I recently purchased a new bag of KNO3 from a supplier and over the course of 3 weeks my tank has turned green!!!!!! Nothing else has has changed as far as I am aware except the KNO3. I have purchased from this supplier before without any issues. So tested a teaspoon of the powder in 1/2 cup of water with my phosphate kit and got a reading close to 5 ppm. My test kit is pretty old (around 6-8 years) so possibly is a false positive, but I wouldn't have thought there was any PO4 in KNO3.... The supplier is positive the powder supplied is KNO3 so I am at a loss as to what to do now... keep dosing with it or get some more from somewhere else Cheers - Peet Quote Link to comment Share on other sites More sharing options...
Adrienne Posted May 29, 2014 Report Share Posted May 29, 2014 There should be 0 phosphate in potassium nitrate. If you are reading correct or near then I would get rid of the lot as clearly there is a mix up and you have no idea what else may be in the mix. Quote Link to comment Share on other sites More sharing options...
alanmin4304 Posted May 29, 2014 Report Share Posted May 29, 2014 Algae problems are often caused by an excess of phosphate over nitrate so I wouldn't have thought that a solution of your nitrate at a teaspoon to a glass of water which is only giving 5ppm in amongst all that nitrate. Plants need phosphate and that is a very small amount. I would doubt that is the cause of the algae. Many cheap fish foods will leave a residual of phosphate. Quote Link to comment Share on other sites More sharing options...
peet Posted May 30, 2014 Author Report Share Posted May 30, 2014 Hi Alan thanks for your response, I'm not sure I'm understanding you though. At the moment I don't think I'm adding any no3 as I think its all po4... Hence there is an excess of po4 over no3. I have run out of nitrate test unfortunately so can't verify Quote Link to comment Share on other sites More sharing options...
amtiskaw Posted May 30, 2014 Report Share Posted May 30, 2014 You could try a flame test. KNO3 will burn violet-red whereas PO4 will flame blue-green Quote Link to comment Share on other sites More sharing options...
peet Posted May 31, 2014 Author Report Share Posted May 31, 2014 Ok, flame test no good.... possibly because both have potassium in them. But I took equal quantities of my Kh2PO4 fert and new bag of "KNO3" in equal volume of water and tested both with the PO4 test kit. Here are my results: "KNO3" Turned royal blue indicating > 5mg/L PO4 content pH = 6.4 KH2PO4 No real colour change indicating 0 to 0.25 mg/L PO4 pH = 4.6. This is correct as H ions create acidity See image above for tests... "KNO3" on the left, KH2PO4 on right. So now I am stumped. The pH of the "KNO3" is correct but the test result is not. I guess for the minimal cost of the fertiliser I will just replace it. Only issue is the supplier wont post. Anyone else have a 1kg of KNO3 they want to sell??? Quote Link to comment Share on other sites More sharing options...
alanmin4304 Posted June 1, 2014 Report Share Posted June 1, 2014 You said you had purchased a new lot of KNO3 so I assumed you were using it as a source of nitrate. My comment was to point out that if you did use it the amount of phosphate in it was minute and since plants need some phosphate as well as nitrate it would hardly make a difference. Quote Link to comment Share on other sites More sharing options...
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