Lowering Alkalinity with Acid

[moonyguy]

Hi Randy

I am trying to lower my alkalinity of Reef Crystals from 13 dkH to ~7 in the hope of using Zeovit products. I got Muriatic Acid to lower the alk of my salt. Do I just add the acid to the water? What can be used to handle the acid? I have a glass dropper from my school chemistry lab can I use it?

My Reef Crystals Alkalinity is 13 dKH. I am using 8.79 ml of acid to drop it to 7 dKH. Does this sound right? My water change volume is 13 gallons (49.21 liters)

Thanks a lot for the help. I really appreciate it.
Vishnu

[smorrow5773]

I am interested in this s well, I do a large change and the new water tends to raise the alk above 9 (I try to keep steady 8) Is there a formula to use for how much to add? What are the consequences, I know alot of CO2 is produced that needs to be driven off, anything else?

[Randy Holmes-Farley]

Yes, you just add the acid. Be very careful with straight muriatic acid. It can easily burn you, especially your eyes.

The "acidity" (that being essentially negative alkalinity) of muriatic acid straight from the bottle is about 11,000 meq/L.

So adding 1/11,000 of the water volume as this acid will drop alkalinity by 1 meq/l (2.8 dKH).

You want a drop of 13-7 = 6 dKH, or 2.1 times that amount, so you'd add 1/5,100th of the water volume.

13 gallons ~ 49 L

1/5100 of 49 L = 9.6 mL

So I'd add 5 ml and stir well for a few minutes and see what alkalinity you get. Then dose again assuming it seems on the right track.

You'll need to aerate well after adding the acid to blow off the excess CO2 and bring up the pH.

[moonyguy]

Sounds good. I will try this and report back. I have goggles for my eyes and will be careful.
Vishnu

[Randy Holmes-Farley]

OK, good luck.

[Jeff]

My tank runs at 12 dkh with a daytime ph of 8.01 (right now with kalk and outside air being bubbled into the tank). Is there a corralation between high alk and low ph?

[MCsaxmaster]

Originally posted by Jeff
My tank runs at 12 dkh with a daytime ph of 8.01 (right now with kalk and outside air being bubbled into the tank). Is there a corralation between high alk and low ph?

No, actually higher alkalinity will favor higher pH. If the alkalinity were lower the pH would be lower than it is now, all else equal. Elevated CO2 is the culprit in depressed seawater pH (assuming the pH reading is accurate, of course).

[Jeff]

I didnt mean to hijack the thread but the ph probe was just calibrated so thats an accurate reading. I cant figure out whats going on here. I have single pane windows in a drafty 100 year old house. I run 2-3 gallons of top-off water daily thru a GEO kalk reactor and have the biggest Whisper air pump sitting outside pushing outside air thru a bubblewand in my sump. My nighttime ph is around 7.7.

[MCsaxmaster]

Hmmm, I'd try a few tests to help diagnose what might be going on:

1) Test the pH in the tank, then scoop out a cup of water and test it a few yards away from the tank or other large electrical devices (making sure to agitate the probe--pH probes need circulation to read properly). This will test for electrical interference with the meter from all the electrical devices used in the tank, which is reasonably common.

2) Scoop out a cup of water and aerate it indoors for an hour or so--see if the pH changes. Make sure that when you retest that the temp of the water is within a degree or two of where it started. Changing the temperature changes the resistance in a pH probe, and thereby changes the pH reading. This will tell us if the tank is near equilibrium with indoor air in terms of dissolved CO2.

3) Aerate a cup or water like above, but outdoors and using outdoor air. Since it's the cold time of year, you may need to warm the water back up to retest (again, should be with 1-2 F of the original temp, ideally). This will test for the chance that the pH reading is inaccurate for some reason. Seawater with the alkalinity you have should have a much higher pH (about 8.4) when in equilibrium with an atmosphere w/ pCO2 ~385 ppm (outdoor air, in other words).

[Jeff]

I have tried Randy's test and the water's ph does increase with outside air. Thats not the problem. The problem is that I have tried everything that has been suggested (kalk and outside air) and my ph still remains low in the display tank. I have also tried running my skimmer's airline outside with very minimal positive results.

[MCsaxmaster]

Do you have or can you borrow a conductivity meter? It may be that you're not getting saturated kalkwasser, which is very common from kalk reactors IME, ironically enough. If not, or as a quick reference, you can use your pH meter for a VERY rough indicator of whether or not the kalkwasser is saturated.

To do so with a pH meter, collect some kalk from the reactor and measure the pH. If saturated the pH should be close to 12.5. However, pH probes aren't particularly accurate at measuring pH over ~10 or so due to cation interference. Anyway, measure the pH of the kalk you're getting. Now mix up a solution that you're certain is saturated: say 1 tsp mixed into 8 oz of water. Measure the pH of the solution that we know for sure is saturated. If the pH of the kalk you're getting from the reactor is lower than the saturated solution then you're getting undersaturated kalk.

A small difference in pH indicates a large concentration difference though. A pH 0.3 units lower would indicate a solution half as concentration. For example, if you got a pH of 12.2 from the reactor but 12.5 from the saturate solution, you're kalk from the reactor is only 50% saturated. Since pH is a log scale, this isn't a terribly precise way to measure the saturation of the kalk. Conductivity is a much better indicator, if you have access to a conductivity meter.

[Jeff]

My kalk is saturated. The kalk isn't the cause of my ph problem, it's simply a fix.

[Randy Holmes-Farley]

Aside from more lime and more aeration with fresher air, there are not many more effective options. photosynthesis with a big refugium will also help, but not usually as much as the other two methods. Somehow removing the CO2 is required.

Maybe don't spend as much time breathing heavily near the tank.

[Jeff]

It's not me Randy. It's the wife. She has a huge set of lungs .

[Randy Holmes-Farley]

OK.

[achillesheel]

how do you dose the muriatic acid?

[Randy Holmes-Farley]

To a tank, or to new salt water. New salt water is easy; dump it in and aerate.

To a tank, I'd dilute it in fresh water (say, at least 10 parts fresh water) then add it slowly to a high flow area away from corals. Depending on how much you are adding, maybe split it into several doses over several days as the pH will drop a lot.

[phillyfishguy]

Randy,

I have muriatic acid 31.45% hydrocloric acid and 20 Baume? The other active ingredients are mostly water but the company I saw on another site, said to them it was moslty water but could be couple ppm of other inert ingredients, since it is commercial grade. I used 15ml of this to bring down alk. I change 50 gallons of water each month. I am in the process now of doing this. Just wondering if this shouldbe okay? I just bought a new bucket of salt and maybe I didn't mix it up, or a bad batch. Its mixed up really high in alk and really high ph.

[Randy Holmes-Farley]

I do not think impurities are likely to be a concern in HCl use this way since so little is added.

[phillyfishguy]

Thank you .

[Randy Holmes-Farley]

Good luck.

[softieatheart]

I know this thread is a little old, but it fits my problem. Could I get a little more info for the noob?

My tank is 5 months old. I have low ph (8 daytime, 1 hour after lights on) and have been using Seachem Reef buffer to bring it up/keep it at 8 as it seems to want to be 7.8.

Everything else was hunuky-dory but then the alk started to climb. I stopped chasing the ph and did some water changes, but alk has been stuck at 13 for the last 3 weeks.

I have muratic acid already for the pool.

Would attempting to lower the alk with the muratic acid be advisable for me? If so, how do I go about it?

Specifics:

46 gallon, bowfront reef tank.
Sumpless
Instant Ocean Salt
Seachem supplements

SG: 1.025
Ph: 7.8
Am: 0
NO2: 0
NO3: 10
Cal: 440
Kh: 13
Phos: 0

ETA: No idea on the Magnesium. I didn't have a test for it and just ordered one today.

[Randy Holmes-Farley]

I personally would not add acid as it will lower the pH even more.

Are you adding any additives at all?

[softieatheart]

Originally Posted by Randy Holmes-Farley

I personally would not add acid as it will lower the pH even more.

I thought that might be the case.

Originally Posted by Randy Holmes-Farley

Are you adding any additives at all?

You mean like Limewater or vodka?

No..... I occasionally add Seachem Reef + or Reef Advantage, but I haven't dabbled in the more advanced stuff yet as I am still pretty shaky on my understanding of the chemistry.

I have been trying to learn, but some of it is just Greek to me, and I am worried about messing up a system that, for the most part, is humming along quite well.

Sometimes it seems like the more I read, the more confused I get. LOL!

[Randy Holmes-Farley]

Don't add any buffers, like the Seachem ones you mentioned as they are alkalinity supplements. Just let the alk decline on its own.