How do I lower the alkalinity?

[Pike614]

I have high KH in my reef tank, and do regular water changes with RODI water. How can I lower the KH?
Thanks!

[tydtran]

Add a little vinegar to the tank. Go slow and check frequently.

[dendro982]

Water changes with salt, that has lower alkalinity - more expensive, but safe, IMHE.

[Frick-n-Frags]

if the reading is whatever 14-16 or less, just let it come down naturally. quit adding whatever to jack it up though.

If the critters are OK with it, you should be too. here again, sudden changes generally should be avoided unless there is no other option(like everything is in severe stress already)

[goldmaniac]

nobody's asked -
How high is your alk?

[Pike614]

about 500ppm

[RA]

What supplements are you adding to your tank? What is your calcium reading?

[Pike614]

NO supplements added at all except for calcium, calcium is stable at 450-490.

[goldmaniac]

ouch

I just had the same problem this week due to some MMLR that hadn't finished curing 100%, and is still slowly releasing carbonate.
But I had a Ca count of only about 300, so last night I added some dissolved Prestone Driveway Heat (CaCl?), which (I understand) lowers Ca at the same time lowering alk a little.

what's your pH? and what's your Nitrates? and what salt are you using for mixing? if you have no supplements, finding the source is pretty imortant. As I said, i'm pretty sure my source for alk was 1) my man-made live rock and 2) normal kalk dosing on top of that. I've cut out the kalk.

as for me, have a low-nitrate tank with a refugium and no protein skimmer. So I'm thinking that the detrius and nutrient breakdown will do a pretty good job lowering alk on it's own. my 'fuge does a good job at keepign nitrates almost to 0 , so i have a little wiggle room with letting nature take it's course. I've been considering stirring up my shallow sand bed in the display a little bit every day, dirtying up, releasing waste, kick starting the nitrate cycle a little more. But I haven't done it. Simply considering it.

I'd do some water changes if I were you. you could do a couple 25% to 33% changes, within a couple days of each other, and get that count down below 400 ppm. after that, if nothing in your tank looks partiularly bad, just cut out the source and everything should return to normal.

again, what salt mix are you adding? no other supplements at all?

[Pike614]

I am using instant ocean for salt, and I am 100% sure that is not the cause because I have another reef tank that has the same salt used and there are no KH issues. I am suspect of some dry base rock I bought that was to be used for reefs. This rock has been in the tank for 3 months now and I was seeding it for use in a larger set-up. I am thinking that there is some mineral in the rock that is causing the elevated KH, and as a resuly an elevated pH also! The pH was about 9 or so I would say, and about 8.6 after a 50% water change. If these elevated levels of Kh continue, I might scrap the base rock afterall. I hope it will come around because the rock is very nice. Not man made, rather taken from dry coral beds.

[goldmaniac]

hmm. interesting. wouldn't have guessed that dry base rock would cause an alk spike, but I can certainly see it happening due to some type of chemistry that i have no experience with.

how about taking it out and just letting it all sit in a trash can of your display's water? you could measure nitrates, pH, alk, all while the base rock would be seeding itself. Just a thought. good luck.

[Pike614]

Basically that's what I've got going, but it is in a 45g tank insted with some more common stuff, ceriths, crabs.....seems like adding vinegar might be a solution, but in the end if the rock is the cause, I suspect this to be a long-term issue.

[goldmaniac]

yeah, I think i actually have alot of info about this. The man-made rock takes months to cure so that it becomes inert, and the only thing that was tested and found to be helpful was actually baking the rocks in an oven over 400 degrees for 5-6 hours. that sped up the carbonation curing. But that doesn't apply to you, I wouldn't think.

The other ideas, vinegar, HCl acid, CO2 bubbles, etc, all were just short-term solutions and futile. vinegar was the closest to being a solution, as it actually did lower pH and alk, but then overnight it would just start climbing again, and you'd be in the same spot.

sorry. I'd think you're thru most of it by now... 3 months is a long time for a soak and I bet most of the leaching is already out.

[Peter Eichler]

What alkalinity test kit are you using? Tell me it's not those little dip stick things...

[Pike614]

when using the test strips, the 5 in one type, the alkalinity test turns almost a neon blue, vs. my reef tank it is a solid dark green color. The strips may not be exact, but they are accurate enough to tell me that I am way off what the norm should be.

[msuzuki126]

salifert ftw

[joelr31]

Have you checked your test kit? High alkalinity and high calcium are a very unusual combination.

[goldmaniac]

if you're using test strips, go splurge $7 on API's Carbonate test. It's the same as alk. Very simple and easy and straightforward.

[Pike614]

ph, ca, nitrates and ammonia kits are API.....
Ca is normal, both pH and KH are the elevated levels