Stop Dosing Phosphates? - The Planted Tank Forum
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post #1 of 4 (permalink) Old 01-09-2016, 02:19 PM Thread Starter
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Stop Dosing Phosphates?

After a recent test, my phosphates are testing in at 10+ppm! That being said, should I stop dosing PO4 on my macro days and just dose Nitrogen and Potassium? Is there any harm in having phosphates this high?
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post #2 of 4 (permalink) Old 01-09-2016, 03:42 PM
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I would stop dosing P until they come down. Also, find the source- have you been over fertilizing? Are you adding some other source of P such as some pH adjusting materials (some pH lowering products contain P)? Fish food? Certain rocks? Is it coming in with the water?

Generally plants use a lot less phosphates than they do nitrogen. Keeping the 2 in a reasonable ratio is usually a good idea. Excess of some nutrients can block the plant from taking in something else. Better to have all the nutrients available in reasonable amounts based on how much the plants use. I have heard of N:P ratios of anywhere from 16:1 to 5:1. Plants are made of about 11.4 parts N : 1 part P (Diana Walstad, Ecology of the Planted Aquarium p 105). You sure do not have to hit that exact value (it would be impossible to do, anyway), but at least have more N than P in the water.
If your soil will hold nutrients, then even less P in the water is just fine. Rooted plants do a very good job of taking P out of the soil.
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post #3 of 4 (permalink) Old 01-09-2016, 03:56 PM
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How confident are you that your test is accurate? Have you done the hoppy calibration?

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post #4 of 4 (permalink) Old 01-09-2016, 04:35 PM
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Agree with most of what Diana said. I would do two additional steps:

1. Test the test kit . Maybe buy a second one, different brand. Do you get about the same result ?

2. Test your fert... add enough to 5-10 L of RO/DI water to obtain 2-3ppm and test to see what the kit says. If you are sure about the fert and the kit says different than the kit is wrong.

Many times when I observe extreme values that I did not expect, I suspect the test kit /test method as well. Also be careful to look at the test result after exactly the amount of time the manufacturer says to.

/* Sidenote: 'most ' and not all just because of a personal view on nature. I do not consider the elemental proportions inside a plant to be a guideline for what should be outside the plant. One would not compare the concentration of Oxygen in the atmosphere or in food with that of the human body. Too simple point of view ? Maybe consider these as well.

1. Most elements are used in very complex molecules inside the plant while some elements are just stored away to be less toxic or as pure storage. So what is the plant might me more than needed, or not needed at all.

2. Different elements concentration/proportion will be found in different organells of the cell, each organell might have different environmental conditions. Even inside the chloroplast you will see very controlled different conditions. Nobody will say a equal concentration of O present as O3, O2 and CO2 is the same for the plant.

3. Proportions will change in different stages of the plants life.

4. Outside the plant elements become unavailable for plants (Fe and PO4), less availabe (NO3 vs NH3 ) outcompete with others for plant uptake, help others enter the plant (Fe and Mg).

As Diana correctly said, there is no need to hit this value. I understand the need to use these type of values as comparison of plant performance but they are not about plant requirements.
*/ End rant.

On hiatus till later this year
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