Safe level of KH2PO4 ? - The Planted Tank Forum
 
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post #1 of 7 (permalink) Old 05-25-2015, 01:14 PM Thread Starter
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Safe level of KH2PO4 ?

I heard from one of our GURU's that using a 1/64 tsp of it gives you more than needed in a 10g tank. And that this fert is one of the main ones which can easily be overdone.
But...I'm seeing symptoms that may be related to not enough of it
according to a thread on deficiencies.
So could I use double that amount in a 10g without hurting anything as long as I do the 50% water changes each week ?
Safe or not ?

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post #2 of 7 (permalink) Old 05-25-2015, 02:50 PM
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Short answer, it would be okay to dose more.

I don't agree with using such small measures when dosing. It's simply not accurate enough.

Let's say you like a teaspoon of sugar in your coffee. Now add the same amount of powdered sugar. Too sweet isn't it? That's because you're actually adding a lot more because there is little air space between the crystals. This just shows that consistency of fertilizers effects the dosage.

When you get down to measures less than say a quarter teaspoon, you're better off mixing a solution IMO.
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post #3 of 7 (permalink) Old 05-26-2015, 10:14 AM
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I think it depends on what you mean by 'safe'.... Safe for plants, fish, safe for the algae-free state of your tank?

I don't use teaspoons (I agree with Zorfox about solutions), but I would estimate 1/64 teasp would be about 0.2g of KH2PO4, which would give you around 4ppm in 10gal. I would vote for safe on all accounts.... More than needed? - maybe... How often do you want to add it?
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post #4 of 7 (permalink) Old 05-26-2015, 12:06 PM
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1 teaspoon of KHPO4 should be about 6 grams, so 1/64 should be about 0.1 g.
Adding 0.1 g into 10g tank (38L) gives you concentration of 1.8 ppm PO4.
I don't say it's safe or not, but I don't know of any scientific paper which deals with the toxicity of phosphates on aquatic critters. That said, I know that even quite small amount of NO3 (1-5 mg/ℓ NO3) can cause increase in mortality with some sensitive kinds of invertebrates (in juvenile stages, fry, fingerlings or fish eggs). Adult fish and invertebrates can tolerate much higher NO3 concentrations (often more than 400 ppm). I would assume that similar results may apply for PO4.

Although 30 ppm NO3 and 3 ppm PO4 can cause no death of adults, it doesn't mean it is safe and harmless for eggs or fry. The increase of mortality of fish eggs or fry due to increased concentration of these nutrients is not something you can easily observe.
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post #5 of 7 (permalink) Old 05-26-2015, 01:17 PM
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I dose my 40b with 1/4tsp 4x a week of K2SO4 KH2PO4 and KNO3 and 3x a week with 1/8tsp of CSM+B. No algae problems, no fauna problems, excessive nutrients don't cause algae problems, alls good in the hood


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post #6 of 7 (permalink) Old 05-27-2015, 02:28 AM
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For several years I have been dosing KH2PO4 at double what the EI tables call for, to control green spot algae. It works fine. No fish problems, but I don't breed fish or have shrimp in my tank.

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post #7 of 7 (permalink) Old 05-27-2015, 02:43 AM
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Quote:
Originally Posted by Hoppy View Post
For several years I have been dosing KH2PO4 at double what the EI tables call for, to control green spot algae. It works fine. No fish problems, but I don't breed fish or have shrimp in my tank.
I do the same, no shrimp either though


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