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yrema
03/07/2008, 07:14 AM
hi all,

Is there a relationship between high PO4 levels and Ph reduction?

bertoni
03/07/2008, 06:56 PM
Phosphate won't affect pH directly. It might encourage algal growth, if the tank would be nutrient-limited otherwise, which might tend to increase the pH swing caused by photosynthesis, depending on the setup.

yrema
03/07/2008, 07:20 PM
thanks bertoni, I was rather confused with the claim that P04 influences ph drop. :)

Randy Holmes-Farley
03/07/2008, 08:34 PM
What did you hear? Some folks claim that certain phosphate binders can cause a ph drop, but that isn't due to the phosphate. :)

Boomer
03/07/2008, 09:23 PM
Is there a relationship between high PO4 levels and Ph reduction?

That depends on how you want to define it. There most certainly is a direct relationship of inorganic PO4's lowering the pH and other inorganic PO4's raising the pH. All one has to due is add some Sodium Biphosphate to their tank. It is often used in lowering the pH in FW tanks. PO4's are also part of the Alk equation. With that said, PO4's in reef tanks have little impact, as they are to low and often may bind with Ca++, when to high, thus lowering them.

Randy goes into detail here

Phosphate and the Reef Aquarium
http://reefkeeping.com/issues/2006-09/rhf/index.php

What is Alkalinity
http://www.advancedaquarist.com/2002/2/chemistry

and

TA = [HCO3-] + 2[CO3--] + [B(OH)4-] + [OH-] + [Si(OH)3O-] + [MgOH+] + [HPO4--] + 2[PO4---] - [H+]

yrema
03/08/2008, 05:19 AM
actually, there's a claim that poor quality AC leaches phosphates and cause a ph drop? :? I don't get it though. Thanks for the link boomer. :)

Randy Holmes-Farley
03/08/2008, 08:58 AM
All one has to due is add some Sodium Phosphate to their tank.

But phosphate that is already in the water is not driving the phosphate down. Phosphate that arises by degradation of organics, as I showed below adds a little acid, but the ongoing contribution is small since the amounts of phosphate added to tank water daily are small:

Phosphate and the Reef Aquarium
http://reefkeeping.com/issues/2006-09/rhf/index.php

from it:

(CH2O)106(NH3)16(H3PO4) + 138 O2 ---> 106 CO2 + 122 H2O + 19 H+ + PO4--- + 16 NO3-

organic + oxygen ---> carbon dioxide + water + hydrogen ion + phosphate + nitrate


actually, there's a claim that poor quality AC leaches phosphates and cause a ph drop?

Some phosphate may come off of activated carbon, and some GAC may lower pH initially by releasing acids improperly left from processing, but hobby GAC does not release enough phosphoric acid for that to be a cause of low pH in a reef aquarium using normal levels of GAC. If it did, the amounts of phosphate added would be unacceptably high. :)

Randy Holmes-Farley
03/08/2008, 08:58 AM
All one has to due is add some Sodium Phosphate to their tank.

So lets follow that up by what reefers do actually add: phosphate from organic materials.

Adding 1 molecule of phosphoric acid by the degradation of organics (shown above) adds a bit over 2 protons (some HPO4-- and a a little PO4---).

So suppose that you add 0.02 ppm of phosphate per day, or 0.02 mg/L = 0.0002 mmole/L. So that adds about 0.001 meq/l of acid

If you add 0.5 mmole/L of acid to tank water the pH drops by about 1.2 pH units as I showed in the article below:

The Relationship Between Alkalinity and pH.
http://www.advancedaquarist.com/issues/may2002/chem.htm

Since we are adding about 500 times less, the pH change is on the order of less than 0.01 pH unit.

Another way of calculating it is to look at the buffering capacity of normal seawater of 0.82 meq/l/pH unit. So 0.001 meq/L will drop pH by 0.001 pH unit:

Boron in a Reef Tank (and its effect on pH buffering)
http://www.advancedaquarist.com/issues/dec2002/chem.htm

So I conclude that there is no relationship between aquarium phosphate levels and pH that normal reefers need to worry about. :)

Boomer
03/08/2008, 11:28 AM
So I conclude that there is no relationship between aquarium phosphate levels and pH that normal reefers need to worry about...............But phosphate that is already in the water is not driving the phosphate down.

I agree and so stated. :D Statements were made and can be read as, that PO4's have no impact on pH which is misleading. So, I wanted to clear the issue ;)

Boomer
03/08/2008, 11:51 AM
..........and hopefully no one will ever add phosphate buffers to their reef tank :lol: Even the FW tank buffers are moving away from PO4 buffers.

GoSixers
03/08/2008, 02:41 PM
Similar question On 03/08/2008 02:34 AM in the phosphate and Ph thread Randy posted, "What did you hear? Some folks claim that certain phosphate binders can cause a ph drop, but that isn't due to the phosphate."

Funny, I just added some phosguard yesterday after tests showed slightly high Phos. and ph has dropped from 8.4 (where it has been since I set up the tank) down to 7.8 right as lights kicked on and slowly rose to 8. I don't know if it’s a coincidence or something else? I realize ph lowers throughout the night and raises as lights are on but my ph has been the most stable parameter so far. I also added 1st part of the calc. recommended dose of reef advantage calcium through the ato last night but if anything shouldn’t that raise ph?

I just pulled out the phosguard after reading what you wrote since phos. dropped as well as ph.

Current parameters

1.023
Ph 7.8-8.0 through out the day
Ammonia 0
Nitrite 0
Nitrate 10 did water change yesterday they were lower before did test twice to confirm?
Phosphate 0 was at around .25 before the Phosguard
Calcium 380
Alkalinity 9

Any Ideas?

Randy Holmes-Farley
03/08/2008, 04:29 PM
I don't recommend Phosguard due to release of soluble aluminum which can irritate corals, but that aside, if there is an effect from adding binders, it goes away with a few days. :)

Randy Holmes-Farley
03/08/2008, 04:30 PM
..........and hopefully no one will ever add phosphate buffers to their reef tank

:thumbsup:

Thanks, Boomer. :)

yrema
03/09/2008, 03:01 AM
thanks randy, boomer. :D

Randy Holmes-Farley
03/09/2008, 04:57 AM
You're welcome.

Happy Reefing. :)

Boomer
03/09/2008, 10:04 AM
Ditto to Randy's last post :D