View Full Version : Need help with massive Ca/Alk consumption

10/03/2017, 07:29 PM
Hi everyone, I've never posted on the forums before, but I am today because I can't seem to find an answer to my question from searching online!

I have a 75 gallon mixed reef that has been running for a few months now. It was an upgrade from an older 50 gallon tank that I did as part of a house move. I have a 20 gallon sump, a Gyre 130, a Vortech mp10, 2 Maxpect Ethereals, a Bubble Magus skimmer and a Jabeo DC return pump. I dose 2 part Seachem Reef Fusion with a Jabeo 4 channel doser.

I'd say my tank should have a healthy demand for Alk and Ca, as I have 2 large grapefruit sized trumpet corals, and about the same amount in bird-nest colonies, as well as some assorted SPS frags and various Euphyllia.
Everything seems healthy and happy in the tank, as long as i keep dosing, but I am currently using 240ml/day of Reef Fusion 1 and 2 (each) to keep the alkalinity and calcium up!! From what I can tell, this should be enough for a large tank heavily stocked with SPS? Right?

My parameters:
Ca: 380ppm
Alk: 6dKH
Mag: 1500ppm
PH: 8.4? (really hard to tell)
No detectable Nitrate/Phosphate

I am using Nutrafin test kits except for mag which is Salifert. I tested the accuracy by testing some freshly mixed reef crystal water, and I got 420ppm and 10dKh with the same kits.

I have noticed some sand clumping, and my heater will develop precipitation very quickly. But if I stop dosing, my tank will plummet to under 5 dKH within the day and my corals become visibly unhappy. Is my pH too high? I added fresh sand when I set the tank up (aragonite), as my old tank was bare bottom. Could the sand bed be causing abiotic precipitation? I removed half the sand and it made no difference on my consumption. I also removed my largest coral colonies and put them in a separate tank for a few days, again with no difference in consumption.

My old tank was maintained with a capflul per day of the same 2 part solution, and the corals have only grown a little bit since then. Now I am dosing 10ml/hour...

Any idea what is going on? I could really use some help on very frustrating problem.

10/03/2017, 08:04 PM

That consumption rate seems far too high. The pH is fine, as are most of the other parameters. The alkalinity is a bit low.

The precipitation on the heater is a bad sign. The sand clumping is a reasonably common occurrence, and might or might to be part of the problem.

I would try switching to baking soda for alkalinity dosing for a bit. The lower pH reduces the tendency for precipitation to occur. I would dilute it with RO/DI, and dose directly into the display tank. Smaller volumes of water will encourage more precipitation. This calculator will help pick a dose:


I would dose the tank up to 7.5 dKH or so in one shot in the morning, and try measuring the dKH about 5 minutes later, to see whether the volume estimate for the tank is correct. After that, if you could measure and dose morning and evening for 2 days, we might get a good trend line. Usually, once a day is fine, but with precipitation problems, a bit more effort might be required at first.

10/04/2017, 07:18 AM
What are you using to test your alk?

Sent from my SAMSUNG-SM-G935A using Tapatalk

10/04/2017, 08:06 AM
While I am not familiar with Nutrafin test kits, the fact that you got 420 ppm Ca and 10 dKH for alkalinity with freshly mixed Reef Crystals seems reasonable.

Abiotic precipitation of calcium carbonate in tank water is a complex process, and is affected by the specific gravity of the tank water, the temperature, the concentration of the calcium & carbonate/bicarbonate ion, the magnesium concentration, and the concentration of organic molecules.

This is what I'd suggest checking:

1) The temperature. If your temperature measuring device is off by a few degrees F, and the tank temperature is actually higher than what you think it is, precipitation of calcium carbonate would be greatly increased. Note that you should measure the tank's temperature and the sump temperature and compare it to your existing device.

2) The specific gravity. You will want to make absolutely sure that your specific gravity is indeed 1.026 by using either 2 different, calibrated devices, or better, take a water sample to an LFS and have them measure it.

If both of these parameters are what you think they are (or close), then I'd suggest several 20% water changes over the course of a week. One or more of the above mentioned concentrations of Ca, Alk & Mg is more than likely not what you think it is, and water changes will have a normalizing effect on the water chemistry.

10/04/2017, 10:28 AM
While I am not familiar with Nutrafin test kits, the fact that you got 420 ppm Ca and 10 dKH for alkalinity with freshly mixed Reef Crystals seems reasonable.

Does it? Isn't RC 490ppm CA and 13 dKH?
regular IO is closer to what they got but not RC

10/04/2017, 11:17 AM
Agreed, but IMO there's a good bit of inconsistency between batches of RC, so I was adding leeway to account for that.

But overall, it's a near certainty that the OP has a miscalibrated measurement somewhere. My bet is on temp and/or salinity, but you could well be right that it's Ca/Alk concentration.

10/04/2017, 03:30 PM
I agree that a measurement problem is a likelihood. I somehow forgot to consider that, or at least post it. Sigh.

10/04/2017, 05:47 PM
Agreed, but IMO there's a good bit of inconsistency between batches of RC, so I was adding leeway to account for that.

I've been noticing that lately.. its always been spot on for me to what they say it should be but lately there have been quite a few posts of it being much lower than what it should be..

I just switched back to regular IO just because I wanted a lower alk mix but it strikes me as odd that a company like that would have so much variation in their mix..

10/04/2017, 07:22 PM
Thanks for all the replies everyone!

I was worried about precipitation clogging my return pump (happened before) so I reduced my dosage to 24ml day of each part last night. I cleaned my heater and I'll watch to see how quickly it returns. When I returned from work today I measured the parameters at:

alk: 5dKH
Ca: 380ppm
Salinity: 1.026 (re-calibrated my refractometer and saw no difference, I'll get it double checked at my LFS soon)

I checked my temperature with a second thermometer. Looking more closely I'd say that my tank and sump are both at closer to 74F. It might be worth mentioning that the water near the bottom of my sand bed is noticeably colder when i put my fingers in it. The tank is in my basement which is pretty cool. Should I turn up the temp?

I was suspicious of how low the Alk reading was, especially because my corals actually look somewhat 'happy' right now. My torch is a bit deflated though, and it tends to be the indicator when my Alk is off, but I would expect a bigger reaction with a dKH of 5. So I mixed some reef crystals again and tested the water. I got Ca at 400ppm, and alk at 7dKH. ...Are my test kits the problem here? What brand should I be buying? My LFS only had Nutrafin and API, and API only came in a kit which is why I went with Nutrafin. I'll mail order something better if I have to. I hear Hannah checkers are good, and Salifert kits as well...

Even if my kit is off by 2dKH, I would still want to raise my Alk to target 9dKH, so I mixed 20g of baking soda into some RO water, dosed into my power head, waited 10 minutes, and measured Alk at roughly 7dKH, which is the increase I expected from the calculator linked above. I'll test regularly and measure my doses of baking soda over the next couple days and report back.

Thanks again everyone.

10/04/2017, 07:32 PM
74 F is a bit low for the animals, but calcium carbonate precipitates more easily as the temperature rises. I'd raise the temperature to 80 F or so over a period of a couple of weeks, but that won't help the precipitation problem.

7 dKH is very low for Reef Crystals, but people do have problems with bad batches or the dry salt settling badly during shipment. I had good luck with Instant Ocean and Salifert kits.

10/04/2017, 10:07 PM
Yes, something is definitely "off" if you mixed a new batch of Reef Crystals to the correct specific gravity and you got those numbers. RC definitely can have some variations batch-to-batch, but an alk of 7 dkH is really hard to explain. In fact, RC is known for having alkalinity that's way too high, and doesn't enjoy a good reputation from the SPS keepers for that reason.

But you should still entertain the idea that your refractometer is out of calibration, because a low specific gravity would explain your salt mix numbers. Keep in mind that a refractometer must be a) made for ocean water (many are scaled for brine) and b) calibrated with a 1.026 calibration solution. Many refractometers will tell you to "calibrate" the instrument with RODI. That won't do it, especially if it's a brine refractometer.

As far as temperature is concerned, 74 deg F is definitely not going to be good for the animals long-term, though they will certainly be OK for a few days. There's a lot of debate about the "right" temperature for coral reef animals, but most will tell you to keep it between 76 deg F and 80 deg F. Too warm is far worse than too cool, btw - anything above 82 deg F is getting into the danger zone. You've several options for accurate temp measurement that won't break the bank. Lifeguard Aquatics little time 'n temp units are quite accurate, and are calibrated from the factory. You can also purchase an accurate laboratory-grade thermometer off of Amazon that should be under $20. With this, you can check whatever electronic instrument you already have, and simply apply an offset.

With respect to alkalinity adjustments, most will advise you that a 2 dKh jump all at once is a bit much - most will recommend no more than a 0.5 dkH adjustment every 24 hours.

Keep in mind the adage that nothing good happens quickly in a reef tank, and apply it to your water chemistry and temperature adjustments. Definitely don't raise the temperature suddenly - that can cause a cascade of bad things that can cause a tank to go downhill fast.

With respect to test kits, a lot of us like Salifert for high accuracy, ease of use, and cost effectiveness. Others may recommend Elos test kits, and Red Sea still has quite a few fans. API doesn't exactly get rave reviews, although in relatively skilled hands they can give accurate results. You can buy Salifert test kits from several 'net dealers and have it by this weekend, one example is Bulk Reef Supply.

01/03/2018, 04:08 PM
Hi All,

It has been a while since the last post, but I thought I would come back and let you all know what happened for the benefit of anyone who might stumble onto this while googling their own alk problem.

I took a sample of water to my LFS, and they confirmed what I been seeing. The salinity was right on, the Ca was okay, but the alk was low. I also noticed they had the same test kit as me, so I went to another store and bought some Nyos test kits. These kits gave a slightly higher alk reading, but not that different.

At a loss, i took the advice of my LFS employee and did a large water change to 'reset' the chemistry in my tank. Probably about 60% as I didn't have a way to mix any more water than that. Then the next day I did another 60%. At this point the parameters for Alk and Ca were normal. about 450ppm Ca, and 9dkh. I then reset my automatic doser to what I thought was more reasonable amount of 2-part for my tank, about 30ml of each per day.

After a week, my Ca hadn't changed, but my Alk went down to about 6.5. So, even though I know this isn't supposed to work this way, I increased the amount of Alk I dose compared to Ca. I think I'm now around 45 Alk and 35 Ca to keep a somewhat constant 400ppm and 8dkh. I'm still fine tuning it.

Anyway, thanks for the help everyone!

01/03/2018, 04:21 PM
Okay, that seems reasonable enough. There are a few processes that will consume alkalinity but not calcium:


Also, our testing is fairly limited in accuracy, so calcium changes might take a long time to show up, if they show up at all. Water changes can have a noticeably impact, for example.

01/05/2018, 08:51 PM
Just skimmed through, and did not catch any conversations about the amount of time between dosing solutions.
I do know if the solutions are dosed too close together, they will precipitate and will be almost ineffective.
I dose 2 part Ca in the afternoon and alkalinity about 2 am I now use less and is much more stable

01/07/2018, 09:24 AM
For the most part, you really don't need to wait anywhere near that long between solutions to prevent an abiotic precipitation of CaCO3 reaction.

In my 20 gallon nano, for example, I manually dose. I add the CaCl2 solution to the display tank, and 30 seconds later or so, add the NaHCO3 to the sump. I don't generally get any clouding that would indicate a precipitation reaction.

01/07/2018, 06:53 PM
The time between doses varies a lot. I dosed into the main display, 2-3 dKH at a shot with matching calcium doses, and waited at most 10 seconds between the doses. If the dose goes into the sump, a much longer wait might be appropriate.