Interaction between bicarbonates and kalk?

Kungpaoshizi · Dec 22, 2016

Hey Randy, hope you're having a good holiday!

I had a peculiar situation come up recently. I usually fight low-er alk touching about 6dkh towards the end of the week before a water change. It's a definite overstocked (with coral) tank. After awhile I'm finding dosing 2 part to not be sufficient as I'm dumping a ton of alk in. (red sea abc stuff)
So I decided to use the remainder of some kalk I have. Things looked great with 6dkh, they still look great to this day, things are growing..
But as time has gone on I've slacked on testing alk, so I test the other day. One test read 4.5dkh and another read 5dkh. But everything looks AMAZING so I'm not really worried about it, but I'm awful curious as to what mechanisms might be causing this. Goniopora, derasa/maximas, few acro's, a mili, lps, few softies, again they all look incredible despite seeing this very low alk reading.

Any ideas on how this might be happening? Dosing includes red sea energy, nopox(underdosing by a good amount), calcium nitrate, red sea A, B, C, and kalk in the topoff.

Thank you sir!

Cory · Dec 22, 2016

I would test your test kits accuracy

Go to a pharmacist and have them weigh out 1.135 grams of baking soda and put it in 1gallon of distilled water. This should read 10dkh.

Randy Holmes-Farley · Dec 23, 2016

I'm not sure why things seem good a low alk, but it may not last.

Here's a copy and paste to show what happens when limewater is added to an aquarium:

The calcium ions in the solution obviously supply calcium to the tank, and the hydroxide ions supply alkalinity. Hydroxide (OH–) itself provides alkalinity (both by definition and as measured with an alkalinity test), but corals consume alkalinity as bicarbonate, not hydroxide. Fortunately, when limewater is used in a reef tank, it quickly combines with atmospheric and in- tank carbon dioxide (CO2) and bicarbonate (HCO3–) to form bicarbonate and carbonate (CO3—):

OH– + CO2 → HCO3–

OH– + HCO3– → CO3— + H2O

Once in the aquarium at an acceptable pH, there is no concern that the alkalinity provided by limewater is any different than any other carbonate alkalinity supplement. The hydroxide immediately disappears into the bicarbonate/carbonate system. In other words, the amount of hydroxide present in aquarium water is really only a function of pH (regardless of what has been added), and at any pH below 9, it is an insignificant factor in alkalinity tests (much less than 0.1 dKH). Consequently, the fact that alkalinity is initially supplied as hydroxide is not to be viewed as problematic, except as it impacts pH (see below).

Kungpaoshizi · Dec 28, 2016

Interesting... I've been wondering if there's another reaction I'm not accounting for.. That would perhaps make some of the alkalinity 'unseen' in the tank according to the two alk tests I have? I'm using the tropic marin and hanna test. Hanna is colorimeter based as you're familiar with, but the TM test is '1 drop of reagent colors the water and equals 1dkh; when the color changes from green to orange, that's the alk'.
I can't recall if it happened pre-kalk, post calcium nitrate addition, but the green color in the TM test has become more see-through than solid green, than it used to be during this process. It was a noticeable difference that I wondered about. But as time has gone on, I can't for the life of me get alk to raise above 6-7. Red sea warns about adding too much of the alk additive, I assume for precipitation, but I'm at a loss. Dosing hourly I'm sure has benefited the tank greatly, but I'm at a point now I'm curious, do I ignore the low alk or acquire a calcium reactor in addition? The thought crossed my mind if there was an unforeseen reaction going on between all the things I'm adding and I'm not actually "seeing" the correct alk content.

I guess I've never seen anyone comment about a ratio of 'total of corals vs gallonage', but I have heard others mention the same as far as 'I can't keep up with alk demand'. Never thought I would be there myself.. Overall thoughts?

Thanks very much for the info Randy!

Here's some decent pics in other threads of my stock, as I said before I'm pretty confused how everything looks this good but according to my tests alk is lower than it should be... (I've hit 6ish alk before and definitely saw everything close up and look much worse, perhaps it's just a delayed reaction or I'm riding a very fine line)
http://reef2reef.com/threads/ecotec...ho-is-seeing-acro-growth-with-radions.279856/
http://reef2reef.com/threads/ever-run-5alk-and-everything-is-ok.279859/

Randy Holmes-Farley · Dec 29, 2016

I don't see any reason to think any alkalinity is unseen.

Are you just using the limewater now, or both limewater and the two part? How much of what?