Rising Alk while dosing ammonium chlorid4e

[keithIHS]

Can I raise pH slightly (~0.2) and lower alk moderately (~1.5 dKH) simultaneously over period of about a week?
My alkalinity has been rising and I don't know why. In this thread, I described how my alk was dropping in a new tank. Probably due to precipitation into the sand and rock (thanks @Randy Holmes-Farley). I then dosed Nitrate to beat dinos and my alkalinity started rising. When it got too high, I switched to dosing ammonium chloride. This worked well for quite some time, but now my alkalinity is rising again. I don't have any corals with hard skeletons, only a few softies, and I'm not dosing anything except NH4Cl. I dropped the alk by lowering the alk of a water change with HCl (24 hours + bubbler to outgas CO2), but it has risen again. It's probably rising about 1 dKH/month.
It would be best to know why it's rising, but I can't figure it out. If you have ideas, I'd love to hear them.
My ultimate goal is to control the alk rise with corals but in order to do that I need to get the alk down so my DT matches my QT, which BTW is too low, so I'm trying to raise the QT alk at the same time.
I could do what I've done before and add HCl to water change water, but I only do water changes every 2 weeks, and I'd like to get it from 10 to 8.5 a little more quickly than 1-2 months, and my water changes are time-consuming so I'd rather not due several during a week. So my idea is to dose HCl directly to the display. I mean why not, I'm already dosing NH4Cl. I understand from Randy's article, "High pH: Causes and Cures", "that adding enough hydrochloric acid to reduce alkalinity by 0.5 meq/L (1.4 dKH) instantly dropped the pH from 8.10 to 6.91." I calculate that at pH 8.0, dosing 1.41 ml of 31.45% HCl to a 130 gal system will reduce alk by 0.086 dKH will lower pH by 0.05. (My dailiy rise and fall is about 0.1 pH.) This will lower my alk from 10 to 8.5 in about 3 weeks.
OK, so if this wasn't sufficiently crazy, I'm wondering if I could dose a higher amount of HCl and dose NaOH to keep the pH up. It would be the insanity trifecta!
But seriously...I know the risks are great. I need to be handling and tracking 3 hazardous chemicals. Aside from the risk, a) is my calculation about the effect of the HCl on pH correct, and b) is there some effect I'm missing that will render this moot or worse. One I'm not sure of is: will NaOH raise alkalinity in some other way than the steady-state equilibrium of alk, pH, and CO2?
Or is there a better way than the above or several water changes to raise pH and lower alkalinity over a period of about a week?

 

[Randy Holmes-Farley]

Dosing NaOH and HCl to the same tank is truly insanity. One raises alk and pH, and the other lowers both. The end result of adding the same amount of each is adding sodium and chloride.

 

[keithIHS]

Thanks, Randy, for keeping me sane. Right HCl + NaOH = NaCl + H2O. I should have seen that. Sigh.

So there's no way to reduce the buffering capacity (alk) while maintaining pH even in an unstable transient situation? I had hoped there was an imbalanced condition that could be created and maintained with low dissolved CO2 and artificially high pH with artificially low alkalinity. I know the air will keep providing CO2 driving the pH down, but can some sort of imbalance be maintained? Or is the only way to do this to get rid of carbon by precipitation (CaCO3) or outgas it (CO2)?

Bicarbonate raises alk but lowers pH, yes? Is there something that does the opposite?

Can I create a slow flow to an aerated reservoir with HCl in the inlet to create very low pH that outgasses CO2, then add NaOH on the outlet to bring the pH up for the display? Yeah, this is getting just a tad complicated, but would this work? Could my aerated slow flow reservoir be my skimmer?

OK, it just occurred to me that I could do a series of small water changes with seriously low alk. How much alk swing can fish, urchins, snails, and softies handle (toadstool, finger leather, tough-as-nails gorgonians)?

 

[Randy Holmes-Farley]

There is no chemical that reduces alk without reducing pH, just as there is no chemical that boosts pH without adding alk (at least at fixed salinity)

Water changes with a very low alk salt mix (or even removable tank water, adjust, and add back) is a good way to lower alk, and the pH effect can be minimized by aerating that mix before using it.

Your slow addition of HCl and NaOH sounds overly complicated and less effective than aerating the water after HCl addition.

 

[keithIHS]

OK, thanks. Any idea why my alkalinity is creeping up? I'm using the same test kit to test new saltwater and water in QT, and they are both a bit low. That's not calibration by any stretch, but it is a little reassuring that hopefully my test kit isn't off.

 

[Randy Holmes-Farley]

OK, thanks. Any idea why my alkalinity is creeping up? I'm using the same test kit to test new saltwater and water in QT, and they are both a bit low. That's not calibration by any stretch, but it is a little reassuring that hopefully my test kit isn't off.

Alk can rise wen demand for alk is low due to falling nitrate, or slow dissolution of rock and sand, or from alk in top off water or a high alk salt mix used for water changes.