DKH 20 Ph 8.2

[Fishing Hobbit]

Having run a medium-sized tank 350Ltr for the past few years I have decided to upgrade. I have no problems with keeping fish but no luck at all with corals. In preparation for the new tank I have started to do far more in the way of testing cleaning ect. most things are going well, alge is being knocked back, etc. I have one puzzle my dkh is stable at 20 and my ph is stable at 8.2. I use no additives or dosing, Can anyone advise me on how to lower the DKH from 20 without effecting the Ph of 8.2

 

[Ron Reefman]

Welcome to Reef2Reef!

BTW, I like the cat in your avatar, I have a flame point Siamese.

What kind of salt are you using? And are you doing water changes with that salt?
Normal dKH should be around 6.0 to 9.0. Lower is hard on some sps corals, but higher seems to be less of an issue. Mine has been as high as 12 dKH and I have a mixed tank (although mostly zoas).

I'd suggest testing your new water for it's dKH (it should be in the acceptable range) and slowly bring it down. You could also add a very small amount of something acidic (like white vinegar) to lower the dKH.

The pH should find it's own level and the dKH shouldn't have much effect at all. The pH is more about the amount of C02 level in the water.

 

[Silver14SS]

How are you verifying the alk is actually 20 dKH? My first thought is an incorrect test result.

If it's truly that high there are directions in this thread to lower it using muriatic acid.

Muriatic acid?

Can I use this to lower ALK in freshly mixed saltwater.? Do I just add a little bit at a time and test until it gets to the level I would like it?

www.reef2reef.com

 

[madweazl]

What is the salinity?

 

[UCF Alum]

I agree that your dkh is not 20. If you’re not dosing or dumping kalkwasser in the tank there’s no way it’s that high. Maybe have your LFS test for you.
@Ron Reefman white vinegar lowers your alk? I've never heard that before. Can you explain?

 

[madweazl]

I agree that your dkh is not 20. If you’re not dosing or dumping kalkwasser in the tank there’s no way it’s that high. Maybe have your LFS test for you.
@Ron Reefman white vinegar lowers your alk? I've never heard that before. Can you explain?

Acids lower alkalinity. I use muriatic acid to lower the alkalinity of Instant Ocean to my desired level but it has a huge impact to pH (sharp drop). I'm guessing he suggested a milder acid to help mitigate this sharp drop (though I had measurable pH drops when I was carbon dosing vinegar).

 

[UCF Alum]

Vinegar does not lower alkalinity at all. Only the pH.
Im assuming he meant muriatic acid.

 

[Randy Holmes-Farley Verified Community Expert]

What do you use to replace evaporated water? If it is tap water, it could be boosting alk constantly.

 

[UCF Alum]

What do you use to replace evaporated water? If it is tap water, it could be boosting alk constantly.

Randy-
Am I correct in saying that vinegar does not lower alkalinity? All research I’ve done indicates it does not have an effect on it.

 

[LAReefer4Life]

I agree that your dkh is not 20. If you’re not dosing or dumping kalkwasser in the tank there’s no way it’s that high. Maybe have your LFS test for you.
@Ron Reefman white vinegar lowers your alk? I've never heard that before. Can you explain?

+1 ^ most likely a faulty test kit. Take it to LFS to verify accuracy or get yourself a second test kit and take it from there

 

[Randy Holmes-Farley Verified Community Expert]

Randy-
Am I correct in saying that vinegar does not lower alkalinity? All research I’ve done indicates it does not have an effect on it.

correct. It will somewhat deplete alk when first added, but as soon as it is metabolized by bacteria or other organisms, it comes back exactly where it started.

 

[Randy Holmes-Farley Verified Community Expert]

Acids lower alkalinity. I use muriatic acid to lower the alkalinity of Instant Ocean to my desired level but it has a huge impact to pH (sharp drop). I'm guessing he suggested a milder acid to help mitigate this sharp drop (though I had measurable pH drops when I was carbon dosing vinegar).

the “strength” of the acid will not impact the pH drop when depleting alk.

 

[Randy Holmes-Farley Verified Community Expert]

The pH should find it's own level and the dKH shouldn't have much effect at all. The pH is more about the amount of C02 level in the water.

That’s not really true. They are both directly related and gave the same effect, but in opposite directions.

a doubling of alk at the same CO2 level will raise pH by about 0.3 pH units.

a doubling of alk and CO2 will offset each other and have no impact on pH.

 

[madweazl]

the “strength” of the acid will not impact the pH drop when depleting alk.

So muriatic acid at 33% and something like vinegar will have an equal impact to pH if dosed at the same rate (for the sake of argument, say 5ml)? I didnt think that would be the case (glad you're here to clear this voodoo up for us).

 

[Ron Reefman]

Sorry for the bad info. I'm a physics guy and should stay away from talking about chemistry.

On the other hand, I learned something about chemistry today... thanks guys!

 

[tdlawdo]

Will any of this change salinity when he tries to correct?

 

[madweazl]

Will any of this change salinity when he tries to correct?

Muriatic acid wont (it doesnt take much) if that is what's used.

 

[Randy Holmes-Farley Verified Community Expert]

So muriatic acid at 33% and something like vinegar will have an equal impact to pH if dosed at the same rate (for the sake of argument, say 5ml)? I didnt think that would be the case (glad you're here to clear this voodoo up for us).

They will have the same effect of dosed in the same actual number of molecules of acetic acetic or HCl, giving the same number of H+ ions when it hits the water.

BUT, table vinegar is only 5% acetic acid while muriatic acid is about 33% HCl, and HCl weighs less than acetic acid, so muriatic acid straight from the bottle gives more H+ than does an equal amount of vinegar. It is the H+ added that lowers alk and lowers pH, so when each is added in an amount to initially lower alk the same, pH lowering will be the same. That is also true of the other main way folks drop alk, sodium bisulfate like Seachem acid buffer.

NaHSO4 --> Na+ + H+ + SO4--

It adds one H+ per molecule dosed, and so has the same pH and alk effect as an added molecule of HCL, even though HCl is a much "stronger" acid than bisulfate (which just means that at very low pH (say, pH 1), the bisulfate will not become SO4-- and H+ but remain as HSO4- giving no pH lowering) while HCl will become H+ at any pH above 0.

 

[Randy Holmes-Farley Verified Community Expert]

Will any of this change salinity when he tries to correct?

Depends on what you add, but never enough to detect with any hobby device and never enough to be concerned with. With muriatic acid, I'm not sure if the effect will even be up or down, since there are two competing effects that are both very small and may offset each other. Only a chemistry geek cares about them, but one is the net effect of swapping a bicarbonate for a chloride and one is the tiny dilution from the added water.

HCL + H2O + HCO3- ---> CO2 + 2H2O + Cl-

 

[Randy Holmes-Farley Verified Community Expert]

Sorry for the bad info. I'm a physics guy and should stay away from talking about chemistry.

On the other hand, I learned something about chemistry today... thanks guys!

If you like physics math, I show the math relationship in this article:

Chemistry And The Aquarium: The Relationship Between Alkalinity And pH

Chemistry And The Aquarium: The Relationship Between Alkalinity And pH

Randy answers many questions in this complex relationship.

www.advancedaquarist.com

The equation results in a graph like this:

Figure 1. The theoretical relationship between carbonate alkalinity and pH for seawater (blue) and freshwater (red) equilibrated with the atmosphere (350 ppm carbon dioxide) using equations 2 and 3.