PH Buffering Capabilities of Randy's Alk Additive

[WVReefJunkie]

Is the ph buffering capabilities of Randy's Alk dosing regiment 8.0, is there other Alk additives in the market that will buffer higher? Iam no Chemistry person, but what chemicals should I be looking for to achieve higher ph? Thanks

 

[Randy Holmes-Farley]

Is the ph buffering capabilities of Randy's Alk dosing regiment 8.0, is there other Alk additives in the market that will buffer higher? Iam no Chemistry person, but what chemicals should I be looking for to achieve higher ph? Thanks

I think you may misunderstand buffering or may be using the term wrong. Probably driven by misleading claims by manufacturers.

pH buffering is the ability of the water to resist pH changes in either direction. It is not really a function of the product used. It is a direct function of the carbonate alkalinity (double the carbonate alk gives twice as much buffering), and is also a function of the actual pH.

That latter part means the pH buffering of seawater is much higher at pH 8.3 than it is at pH 7.8. One consequence of that effect is that it is much easier to have stable pH at higher pH than at lower pH in a reef aquarium.

As to additives, they of course boost alkalinity, which impacts buffering, and they can also tend to raise or lower pH.

A sodium bicarbonate alkalinity additive will tend to lower the pH a little bit, no matter the actual tank pH.

A sodium carbonate or hydroxide alkalinity additive will tend to raise the pH, and hydroxide raises it about twice as much as carbonate, no matter the actual tank pH.

With a mixture of carbonate and bicarbonate, the ratio between the two, as well as the actual tank pH will determine whether adding that mixture actually raises or lowers pH, or has no net effect. A mix of mostly bicarbonate and a little carbonate may have no net pH effect at pH 8.2, but will slightly lower pH if the tank pH is higher than 8.2, and will slightly raise pH if it is lower than 8.2.

That is the kernal of truth behind the ridiculous claims that some manufacturers make that their product "buffers the tank to pH 8.3" or some such thing. It does not mean that once added that the tank is any more likely to maintain pH 8.3. It isn't. it just means that for the initial seconds after it is added, the pH is driven toward that point.

Some folks mistakenly think such a mixture is inherently desirable, and I think that is generally not true. if your pH runs low (most common), then using carbonate or hydroxide alone will do the most to help your tank.

If the pH runs high (say, if you also use limewater/kalkwasser), then bicarbonate may be best. Lower pH and hence bicarbonate may also be best if the goal is to minimize abiotic precipitation of calcium carbonate.

Thus, alkalinity additives do not really buffer to a pH in seawater. They only tend to raise, lower, or leave pH unchanged, and you can essentially elect the effect that most suits your needs.

Note that I simplified the discussion by ignoring the effect of borate, but the conclusions are unchanged and I do not think borate should be put into normal reef aquarium alkalinity additives.

This article has much more on buffering of seawater:

Chemistry And The Aquarium: Boron In A Reef Tank

This article also discusses the sources and sinks for boron in reef tanks, and shows that while typical tanks may be slightly depleted in boron with respect to natural levels, most are not so significantly depleted that any correction is required. Nevertheless, how to test for and supplement...

reefs.com

Hope that helps!