Alkalinity / dKH

[Spongebob]

I'm sure you've answered this one a thousand times, maybe it would be easiest to refer me to an earlier thread...

My alkalinity (in dKH) came out at 4 today!

I understand that low alkalinity will tend to exacerbate fluctuations in pH, so I used Kent buffer in an attempt to bring it up. It worked, but I hate to dump chemicals in my tank, particularly in pursuit of something I scarcely understand.

What causes KH to fall in the reef tank? What exactly are KH and alkalinity? Should we manually buffer our tanks to achieve a particular reading?

Thanks for any advice / enlightenment you can offer.

[Randy Holmes-Farley]

Spongebob:

<< What causes KH to fall in the reef tank? What exactly are KH and alkalinity? Should we manually buffer our tanks to achieve a particular reading? >>

I just submitted a detailed article on alkalinity to AAOM, and it likely will be posted there by mid February:
http://www.advancedaquarist.com/issues/jan2002/toc.htm

In short, corals and other organisms in your tank use carbonate (CO3--) (or close relatives thereof, like bicarbonate; HCO3-) to make calcium carbonate (CaCO3) skeletons. You will need to constantly add both calcium and some sort of carbonate replacement.

There are many ways to supplement alkalinity, which is a surrogate measure for bicarbonate and carbonate, and there must be 50 different commercial products for doing so.

[Spongebob]

Thank you for the succinct answer! So "alkalinity" means "carbonate content" i.e., the concentration of --carbonate compounds in the water, and needs to be supplemented artificially. No problem...

Well, maybe one.

Is there a non reef-oriented product that can be used instead of commercial buffer products, e.g., baking soda? Kent Marine Buffer seems to be a good product but rather expensive. Thanks again.

[Randy Holmes-Farley]

<< So "alkalinity" means "carbonate content" i.e., the concentration of --carbonate compounds in the water, and needs to be supplemented artificially. No problem...>>

In a crude sense, yes.

<< Is there a non reef-oriented product that can be used instead of commercial buffer products, e.g., baking soda? Kent Marine Buffer seems to be a good product but rather expensive. Thanks again.>>

The commercial products, especially the two part additives, have some big advantages, but you can use other things:

Baking soda (sodium bicarbonate) alone is OK, but tend to lower the pH.

Washing soda (sodium carbonate)alone is also OK, but raises the pH a lot.

A mixture of mostly baking soda and some washing soda is an alternative that some people use.

[aLittletank]

FWIW the ratio I have read was 6 to 1 (baking to washing)

[Mako]

Here is a link to the homemade buffer.

http://www.hawkfish.org/infoctr/homebuffer.htm

[Randy Holmes-Farley]

If you follow that 6:1, make sure that what you are using actually is washing soda (sodium carbonate decahydrate), and not anhydrous sodium carbonate (which is 2.7 times as potent).

[alexander]

Hi, We exchanged a few posts about 3 days ago on a similar comfusion. I had added baking soda because my pH was 8.0 and it raised my alk. and did nothing to pH. You replied that 8.0 wasn't so bad. I'm still confused: this thread says baking soda will actually lower pH, but I've also read that a good way to prevent pH drop is to use 1 tsp/20 gallons/week . After a few days of adding nothing my alk and Ca are both dropping, so I'm resuming the Kent 2-part supplement with their CaCl additive also, and throughout all this my pH has stayed at 8.0. Will more frequent h2o changes alone help the pH rise to the 8.2-8.4 level that's usually recommended? What, if anything, would you advise to use a pure buffer other than than the 2-part supp.? Thanks for your time/help!

[Randy Holmes-Farley]

Alexander:

<< You replied that 8.0 wasn't so bad. I'm still confused: this thread says baking soda will actually lower pH, but I've also read that a good way to prevent pH drop is to use 1 tsp/20 gallons/week . >>

You didn't think something could both raise and lower pH, did you!

But that's the source of the confusion!

When you first add sodium bicarbonate to a tank, the pH drops. This is true for every tank with a pH over about 7.7.

What happens is that some of the bicarbonate breaks up into H+ and carbonate (CO3--).

The H+ lowers the pH.

However, because you added bicarbonate, you raised the total dissolved CO2 (H2CO3/HCO3-/CO3--).

Over time (hours to days) the system will reequilibrate itself, and blow off the excess CO2, raising the pH again.

Still, this isn't the effect that people are talking about "raising the pH". Even if the process is perfectly complete, the rise in pH is small.

What they are typically referring to is preventing a pH drop as calcification occurs in corals. This procedss consumes carbonate and drives down the alkalinity, and hence the bicarbonate and carbonate).

Consequently, the "rise" on adding baking soda is more like preventing a drop, rather than a big increase.

Think of it this way:

The endproduct of calcification is to remove carbonate.

The immediate product of bicarbonate addition is to add bicarbonate which equals carbonate + acid.

The combination of these two effects is to add acid.

Fortunately, the acid added can be blown off as CO2 over time, so does not build up forever, continually lowering pH.

Nevertheless, using just bicarboante every day will result in a lower tank pH than if you simply replaced exactly what the corals consume.

Hope this helps........:)

[alexander]

Randy: It does help and I appreciate your patient explanations!!
And, amazingly, I'm still unclear on just one thing!: If the pH doesn't rise above 8.0 after a while(how long should I wait?), then do I just do more h2o changes(I've never checked th pH of a new batch of Instant Ocean), or add some kind of buffer like Proper Ph 8.2? I can be much more patient if I know the time frame of the process I'm monitoring. Thanks again!

[Randy Holmes-Farley]

Alexander:

CO2 will blow off in a day or two. Don't be too patient:D

Instead of an additive that claims to keep a certain pH (which is just the mixture of bicarbonate and carbonate existing in seawater at that pH), you should add something that raises pH if raising the ph is the desired goal.

Limewater, washing soda (sodium carbonate), or B-ionic (the original version) are all good choices.

[alexander]

Thanks Randy! I assume limewater is the same as pickling lime and avail. at the supermarket?

[Spongebob]

Alexander,

I think Randy will second this. Yes, pickling lime is calcium hydroxide, i.e., Kalkwasser powder.

The only difference that I know of (and I guess I don't really know this to be a fact, but it seems plausible and I've heard it on more than one occasion) is that the stuff sold for reef is a finer powder. But you should probably take that with a grain of salt.

[Randy Holmes-Farley]

It is the same chemical, yes. Different grades may have different impurity profiles, but people seem to use most grades without problem. I'd suggest not using anything that isn't white, and don't dose milky limewater if the grade is marginal. I'd avoid agricultural grades unless i knew more about them.

Personally, I use CaO (calcium oxide; quicklime), which is a slightly different chemical, but gives the exact same thing once in water.

[alexander]

Thanks, Randy et al, I've resumed dosing with the Kent 2-part and Kent CaCl; my alk =3.3 and Ca=420 which seem right on; Ph is still hovering around 8.0-8.1 with the Salifert kit which has a huge color jump between 8.0 and 8.3. Should I increase the amnt. of the 2- part to raise pH even tho the alk/Ca are both OK? You said not to be too patient, Randy; it's been about a week with the pH hovering aroud 8.0. I do have considerable surface agitation with an Eheim spray bar, a CPR skimmer and a Magnum just for carbon, so lots of ways to blow off co2 I would think....

[alexander]

RAndy, P.S.: How would the original B-ionic be equiv. to limewater or washing soda? Did you mean just using the alk component? I've been using a 2-part without any rise in pH...maybe you're saying the Kent and ESV brands have different effects on pH?!? Just when I thought I almost understood this stuff a little bit....

[Randy Holmes-Farley]

Alexander:

<< Should I increase the amnt. of the 2- part to raise pH even tho the alk/Ca are both OK? >>

I may be getting various threads confused, so forgive me if that's the case.

Your calcium is now OK, so you don't need the Kent calcium in addition to the two part additive, unless part of the two part additive is what you meant by Kent calcium.

I think if you just keep using the Kent two part additive, you'll be fine. I'm not really sure how much of a pH raising effect it has relative to B-ionic. Perhaps the Kent product is similar to the new version of B-ionic (the bicarbonate version) and not the original.

Anyone ever compared these two in that fashion?

Alexander, if you measure its pH (the alkalinity part of the two part additive) we can tell how much of a pH raising effect it will have.

Limewater will have an even bigger effect than any of these.

Overall, I wouldn't worry too much about pH 8. It's 7.8 and below that begins to worry me.

[alexander]

Randy, Why didn't I think of that? Because I'm not a chemist?! Anyway the pH of the alk component of the Kent. 2- part is 8.4- with Red Sea and maybe 8.5-8.6 with Salifert kits. The main reason I'd like to get the pH up is to get my xenia pulsing again(they haven't stopped entirely but slowed way down). I came to the same conclusion about stopping the Kent CaCl so I'm just using the their 2-part, in slightly higher doses and testing daily. If I were to go the limewater/kalkwasser route , would I just start with very low doses in addition to the Kent and keep testing or is there some rough rule of thumb? Can't tell you how much I appreciate all the help/advice/patience!!!!!

[Randy Holmes-Farley]

<< Anyway the pH of the alk component of the Kent. 2- part is 8.4- with Red Sea and maybe 8.5-8.6 with Salifert kits. >>

OK, that's quite low (assuming that you did not max out those kits; anyone with the Kent product and a pH meter that can measure it for us?. If real, that pH is more like the new B-ionic. The original B-ionic will have a MUCH higher pH and will raise the tank pH a lot. I didn't realize that Kent's was so low....Maybe that was the driving force behind a new B-ionic....(or perhaps the other way around).

If you like the two part system (it's a good system, IMO) and want to raise pH, try the original B-ionic at www.esvco.com ).

<< If I were to go the limewater/kalkwasser route , would I just start with very low doses in addition to the Kent and keep testing>>

Yes, that's what I would do if you want to go this route. Use the two part for most of the additions, and just enough limewater to bring up the pH.