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Zaphodent

advice on low dKH

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My Hanna checker shows an alkalinity of 63 ppm which comes out to 3.5 dKH. I tested it 2 days later just to make sure the trend was within the same area, 76 ppm which is a 4.2 dKH. 

 

Corals are doing fine from appearance and not sure how low my dKH has been since I've never really tested for it besides calcium. I started dosing a few months ago after moving to a monthly water change (instead of every 2 weeks, got tiring). My calcium at one point was less than 300. I have a few large corals that consume calcium. 

 

My calcium today is around 450, magnesium 1250. I dose B-ionic 2 part. 

 

To get a baseline, I tested a fresh batch of water (red sea coral pro). dKH is 11 and magnesium was 1450-1500 (using red sea mg test kit). The high magnesium is normal with red sea coral pro from what I remember. 

 

My pH is normal but does have a wide swing. Ranges between 7.8 to 8.4 from night to day, see pic attached. 

 

 

Any thoughts on why my dKH is low?

 

post-2636149-0-18092600-1516165475_thumb.jpg

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While alkalinity typically doesnt affect pH in the aquarium to much degree, having it that low may exacerbate the delta between day and night provided your probe is actually correct, when was the last time you calibrated it? From what I'm seeing online, RSCP seems to mix in the 12-13 dKh range so you may have some test error responsible for a portion of that low number as well; probably worth having a buddy or LFS check a sample if you dont have another kit to compare the results with. I got tired of trying to line up the meniscus of the sample at the line on the Hanna cuvette so now I just use a syringe and add 10ml (easier and likely more consistent sample to sample now) 

 

I'm assuming you're dosing alkalinity and calcium equally with the B-Ionic? Just because they're consumed at equal rates doesn't mean they'll be dosed at equal rates. They could have started at ranges that differed from your target in the beginning as well. If your calcium levels are stable and where you want, AND your alkalinity is actually down in the weeds, increase the dose of your alkalinity to slowly bring it into the range you desire and then cut it back to maintain that level was you get there. 

 

Also, what is your salinity? 

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With low alkalinity, you're likely to see wider pH swings since there is less buffering capacity. You should see your pH swings narrow some once your alk is back to reasonable levels.

 

How did your alk get so low? It's low enough that I'd suggest a series of water changes to bring it back up. Salinity is an important question to answer, but it won't answer why you're so low right now (with corals looking fine).

 

What kind of corals do you have in this tank, anyway? Softies? LPS? SPS? (Most, if not all, SPS would probably not tolerate such low alk for any extended period of time.) 

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While alkalinity typically doesnt affect pH in the aquarium to much degree, having it that low may exacerbate the delta between day and night provided your probe is actually correct, when was the last time you calibrated it? From what I'm seeing online, RSCP seems to mix in the 12-13 dKh range so you may have some test error responsible for a portion of that low number as well; probably worth having a buddy or LFS check a sample if you dont have another kit to compare the results with. I got tired of trying to line up the meniscus of the sample at the line on the Hanna cuvette so now I just use a syringe and add 10ml (easier and likely more consistent sample to sample now) 

 

I'm assuming you're dosing alkalinity and calcium equally with the B-Ionic? Just because they're consumed at equal rates doesn't mean they'll be dosed at equal rates. They could have started at ranges that differed from your target in the beginning as well. If your calcium levels are stable and where you want, AND your alkalinity is actually down in the weeds, increase the dose of your alkalinity to slowly bring it into the range you desire and then cut it back to maintain that level was you get there. 

 

Also, what is your salinity? 

 

Salinity is 1.025 and my pH probe is good. I calibrate by refractometer and probe every six months, thanks to digital reminder apps. 

 

RSCP at 12-13 dKH, I imagine would also depend how much salt we're mixing to make a water batch. I do mine at 1.025 so 11 sounds about right?

 

I just increased the timer for the alkalinity dosing so gonna try to monitor that. Thanks for the feedback. I'm monitoring the magnesium as well. I haven't had to dose that since my ranges seem within reference values but RSCP is so high to begin with so wondering if that is affecting my dKH. 

 

 

With low alkalinity, you're likely to see wider pH swings since there is less buffering capacity. You should see your pH swings narrow some once your alk is back to reasonable levels.

 

How did your alk get so low? It's low enough that I'd suggest a series of water changes to bring it back up. Salinity is an important question to answer, but it won't answer why you're so low right now (with corals looking fine).

 

What kind of corals do you have in this tank, anyway? Softies? LPS? SPS? (Most, if not all, SPS would probably not tolerate such low alk for any extended period of time.) 

 

Not sure how it got that low, was surprised. I did dose calcium a bit higher to catch up at one point but wasn't monitoring dKH until I ordered more refill agent.  But there is definitely a wide swing in pH. I have easy to care for SPS like birdnest and monti caps but their big enough to consume a decent about of calcium. LPS and softies also in the tank. I have a hammer the size of a human head but it seems to be doing fine. 

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What test kit are you using? Do you trust it? Have you cross-checked it with any other kit?

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If it's been six months since the last calibration, it is likely off by a decent margin but I dont know that it would cause a larger swing (my pH levels typically just creep higher with a similar delta night to day as the calibration fades). 

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If it's been six months since the last calibration, it is likely off by a decent margin but I dont know that it would cause a larger swing (my pH levels typically just creep higher with a similar delta night to day as the calibration fades).

Larger swing comes from less buffering capacity (bicarbonate provides buffering << Wikipedia link on buffering agents) because of a lack of carbonate alkalinity. Buffering moderates wide pH swings around a target point. With less bicarbonate, the pH in your tank is free to swing over larger ranges rapidly.

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