Ph drop in my 20 gal - The Planted Tank Forum
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post #1 of 13 (permalink) Old 09-05-2017, 12:28 PM Thread Starter
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Ph drop in my 20 gal

Hi all,

My tap water is pH 7.0 - 7.2

I've discovered that it is my KH2PO4 dosing, that is causing my pH to drop below 6.0
I'm afraid with CO2, the pH has dropped even further.

What shall I do?

Do I need to put corals to push up the ph?

Use baking soda?

Thanks

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Last edited by NightHedgie; 09-05-2017 at 09:46 PM. Reason: Update
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post #2 of 13 (permalink) Old 09-06-2017, 04:44 AM
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Sounds like you have very little if any KH which is causing the PH to fluctuate very easy. What is your KH?


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post #3 of 13 (permalink) Old 09-06-2017, 02:11 PM Thread Starter
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Originally Posted by clownplanted View Post
Sounds like you have very little if any KH which is causing the PH to fluctuate very easy. What is your KH?
Probably 1 dKh

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post #4 of 13 (permalink) Old 09-06-2017, 07:51 PM
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Switch from KH2PO4 to KPO4. KPO4 is commonly used in aquarium not KH2PO4.
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post #5 of 13 (permalink) Old 09-06-2017, 08:29 PM
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Originally Posted by Surf View Post
Switch from KH2PO4 to KPO4. KPO4 is commonly used in aquarium not KH2PO4.
KH2PO4 is what is commonly used, not KPO4, KPO4 is erm... how do we say this, not a real chemical? It might be possible to technically produce it but it will only exist for a very short period of time before degrading into other material, it has too much of an inequal charge distribution. The molecule would be extremely unstable, as phosphorus can only form 5 covalent bonds. KPO4 would immediately deprotonate any material it came into contact with. (almost anything)
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post #6 of 13 (permalink) Old 09-07-2017, 01:18 AM
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KH2PO4 is what is commonly used, not KPO4, KPO4 is erm... how do we say this, not a real chemical?
Sorry K2PO4, potassium Phosphate. The vast majority of people using EI fertilization methode are using potassium phosphate. KH2PO4 is Monopotassium phosphate. What is happening here is plants are consumming the potassium leaving H2PHO4 behind H2PO4 with then quickly converts to H3PO4 which is phosphoric acid and PH goes down.
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post #7 of 13 (permalink) Old 09-07-2017, 01:49 AM
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Probably 1 dKh

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Unless you have a buffering substrate it takes very little to cause a PH swing like you are seeing with that low KH. I suggest either a buffering substrate or raising that KH at least 1 more to give you 2.


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post #8 of 13 (permalink) Old 09-07-2017, 02:35 PM Thread Starter
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Quote:
Originally Posted by Surf View Post
Sorry K2PO4, potassium Phosphate. The vast majority of people using EI fertilization methode are using potassium phosphate. KH2PO4 is Monopotassium phosphate. What is happening here is plants are consumming the potassium leaving H2PHO4 behind H2PO4 with then quickly converts to H3PO4 which is phosphoric acid and PH goes down.
I won't see a ph drop with k2po4?

I can't seem to find k2po4, there is a k2hpo4 on rotala butterfly

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Originally Posted by clownplanted View Post
Unless you have a buffering substrate it takes very little to cause a PH swing like you are seeing with that low KH. I suggest either a buffering substrate or raising that KH at least 1 more to give you 2.
Using baking soda?

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Last edited by Darkblade48; 09-09-2017 at 04:48 PM. Reason: Please use the edit function for back to back posts to keep threads cleaner
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post #9 of 13 (permalink) Old 09-07-2017, 03:53 PM
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Using baking soda?

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Yes that is one way to do it for sure.


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post #10 of 13 (permalink) Old 09-07-2017, 04:20 PM Thread Starter
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Yes that is one way to do it for sure.
How shall I go about it? After the co2 and kh2po4 makes the ph drop, I put baking soda to make ph rise to say 6.4 ph? Or just make it go up 1dkh. Say 2 dkh?

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post #11 of 13 (permalink) Old 09-08-2017, 04:21 PM
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Quote:
Originally Posted by Surf View Post
Sorry K2PO4, potassium Phosphate. The vast majority of people using EI fertilization methode are using potassium phosphate. KH2PO4 is Monopotassium phosphate. What is happening here is plants are consumming the potassium leaving H2PHO4 behind H2PO4 with then quickly converts to H3PO4 which is phosphoric acid and PH goes down.
That's not how it works.

K2PO4 also does not exist, as the phosphate anion has a -3 charge.

You can have either the monopotassium phosphate (KH2PO4) or dipotassium phosphate (K2HPO4).

For either form, even in the absence of plants, upon dissolution, the cation and anion would disassociate, causing slight changes in the pH. It is implausible for plants to instantly use up the potassium, leaving behind the phosphate anion to reduce the pH.

Anthony


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post #12 of 13 (permalink) Old 09-08-2017, 06:48 PM
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Quote:
Originally Posted by Surf View Post
Sorry K2PO4, potassium Phosphate. The vast majority of people using EI fertilization methode are using potassium phosphate. KH2PO4 is Monopotassium phosphate. What is happening here is plants are consumming the potassium leaving H2PHO4 behind H2PO4 with then quickly converts to H3PO4 which is phosphoric acid and PH goes down.
Yeah this is not true.
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post #13 of 13 (permalink) Old 09-08-2017, 07:32 PM
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Yeah this is not true.
Ya I gave up trying to convince him otherwise in the other thread he was preaching this same wrong thing haha.


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