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Old 07-10-2019, 07:15 PM  
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Default Phosphorus and Phosphates

I'm trying to address some macro-nutrient deficiencies in my plants. I think I have it figured out for the most part--except for phosphorus.

Whenever I have dosed phosphorus in the past in the balanced amount to go along with the other macro-nutrients (nitrogen, potassium) I have always ended up with an algae bloom. I thought I might have a lot of phosphates in my tap water. I can see how phosphates in my tap water plus dosing phosphorus could be "over-dosing" and lead to algae blooms. Does this logic sound correct?

I tested the phosphate level in my tap water using API's test kit. I'm not sure if I am reading the test results correctly. Maybe one of you can help? If I follow the instructions exactly and look at the color after 3 minutes, then the result is 0-0.25ppm. But, if I let the test tube sit for an extra 3 minutes or so the color continues to darken. It eventually turns into an opaque forest green color (no color on the results chart). I retested it in a different clean test tube to be sure it wasn't a fluke and had the same dark color/results. Does this mean that the actual phosphate level in my tap water is very high?

Tap Water Parameters
GH = 1-2 German degrees
KH = 2 German degrees
Phosphate = 0-0.25ppm(or higher?)
pH = 6.8-7.0
Nitrite = 0ppm
Nitrate = 0ppm
Ammonia = not tested
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Old 07-11-2019, 09:20 AM  
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Default Re: Phosphorus and Phosphates

As a general rule, you have to follow the instructions that come with a test kit, exactly as written, or you can't rely on the results of the testing. But, I have no experience with measuring phosphates, so I don't know the answer to your question.
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Old 07-11-2019, 04:05 PM  
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Default Re: Phosphorus and Phosphates

Instruction says to wait 3 minutes for the color to develop.
Yes, tap water can contain phosphate type chemicals. Your municipal add triphosphate salts in the water to help with pipe corrosion.
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Old 07-12-2019, 04:36 PM  
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Default Re: Phosphorus and Phosphates

I've heard that phosphates can be added to tap water as a buffer, but I didn't know phosphates also help with pipe corrosion. Interesting!

I'll go with the reading at the 3-minute mark then, which was somewhere between 0-0.25ppm based on the color chart. Which means I need to dose phosphorus after all!

Thanks.
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