Alk drops consistently, however Calcium and Mag stay high, why?

[AZMSGT]

The back ground:
I started my tank in July 2019, first livestock went in about mid Oct. Coraline has been building steady since late Nov. At that time I added my first test SPS coral, a green slimmer staghorn. Since then I have added 25 other SPS corals as well as some Zoas and Hammer corals.

For reference, many SPS are encrusting and the slimmer has grown 1”. So from what I can see the corals are using Calc. Colors look good for the most part. Some reds are weak. Most of the SPS are getting 210-240 par at 9” below the waterline. I’m slowly increasing lighting with a goal of 350 around 3” from the top waterline. (Just seems like a good number at that height.) The tank is 24” tall and waterline is at 22”

PH is 7.8 - 8.2 through the day.

I use Tropic Marin Pro and am set up to do AWC at .6gal 4 times a day. The tank is 130g and 35 in the sump.

The Problem/question
Alk drops steady at 10ml per day or .1 however Calcium and Mag are holding high and steady at 500 and 1470 respectfully. Cal and Mag are tested with salifert test kits. They are high according to everything I have read.

I assumed that I should see an equal drop in Calc and Mag with the usage of Alk. Is this not the case?

To keep the Alk at 8-8.1 I have dosed Red Sea Alk.

My assumption is I will start seeing more Calc and Mag usage soon as the corals seem to be settling in. But that’s just an assumption.

Thanks for any insight you guys can provide.

 

[William Mumford]

sounds like you need to add a co2 scubber. It was the best 40 dollars I have ever spent. I suggest makeing yourself a recirculating co2 scubber to keep the media replacement to a minimum super simple and so effective. An easy way to see if it will help is take a sample of your water test the ph put the sample outside for an hour check that same sample if it rises the co2 scubber will work. Also another good test to see if it is co2 related is to open your windows in your house for a while and see if the ph rises if it does co2 scubber will fix your problem more than likely. I really enjoy a co2 scubber addition because you are not doing anything chemically to the tank and they work.

 

[lapin]

To quote Randy
"If you drive alk up you will add 20 ppm calcium for each 2.8 dKH of alkalinity, so I do not think it will immediately boost calcium too much. Very long term, calcium will rise a bit more"

 

[William Mumford]

When alk is higher coral use all nutrients more so when your ph swings. I would think that when the ph is lower it uses less giving you the results that you are seeing. When the alk stays consistent I think you see much more even results in usage.

 

[nereefpat]

Not sure what a CO2 scrubber has to do with OP's question.

0.1 dKH only will equate to a drop in Ca of less than 1ppm. You can't measure that with a test kit. Also, your water changes are keeping up with Ca consumption.

 

[William Mumford]

Not sure what a CO2 scrubber has to do with OP's question.

0.1 dKH only will equate to a drop in Ca of less than 1ppm. You can't measure that with a test kit. Also, your water changes are keeping up with Ca consumption.

It will help with the alk dropping. If the alk doesn't change like it is. Then you won't have the issue. An ounce of prevention is worth 1000000 pounds of cure. The swing is the problem not the consumption.

 

[DoctaReef]

I'm doing auto water changes with Tropic Marin Pro too and have dealt with similar issues. The AWC is a variable you have to consider.

Two things, and forgive me if you knew this already:

1. Tropic Marin Pro mixes at a dKH of 7, so if you are doing an AWC, you are losing Alkalinity unless you've balanced the new salt mixture by adding it to the new water. I use Trident controlled dosing with a Dos, and it does it for me in the tank to maintain Alk between 8.3-8.5 dKH.

2. Alk is used up in greater proportion to Ca, when the coral grow, so you will see a higher swing in Alk even without water changes, so you may not see significant changes in Ca for a while especially if you are replacing it daily with the AWC.

As a side note, I've always thought about opening my old Chemistry textbooks to try to figure out how to isolate Ca and Alk consumption from the total amount I've needed to add with an auto water change. There's got to be an equation!

 

[AZMSGT]

I'm doing auto water changes with Tropic Marin Pro too and have dealt with similar issues. The AWC is a variable you have to consider.

Two things, and forgive me if you knew this already:

1. Tropic Marin Pro mixes at a dKH of 7, so if you are doing an AWC, you are losing Alkalinity unless you've balanced the new salt mixture by adding it to the new water. I use Trident controlled dosing with a Dos, and it does it for me in the tank to maintain Alk between 8.3-8.5 dKH.

2. Alk is used up in greater proportion to Ca, when the coral grow, so you will see a higher swing in Alk even without water changes, so you may not see significant changes in Ca for a while especially if you are replacing it daily with the AWC.

As a side note, I've always thought about opening my old Chemistry textbooks to try to figure out how to isolate Ca and Alk consumption from the total amount I've needed to add with an auto water change. There's got to be an equation!

This is the answer that fits my situation and seems logical considering my set up. Thanks.

 

[DoctaReef]

This is the answer that fits my situation and seems logical considering my set up. Thanks.

You’re welcome. Good luck.
Mines just like yours, only smaller, a RSR 425XL.

 

[YankeeTankee]

I assumed that I should see an equal drop in Calc and Mag with the usage of Alk. Is this not the case?

No this is not the case if I understand you correctly.

While Ca and Alk are used by corals at basically 1:1, this is not reflected in our tests. This is because there is way more Ca in seawater than Alk so the percentage drop is less for Ca and more for Alk. This is what Lapin was saying with the quote about 2.8 dkh Alk and 20ppm Ca.

 

[Randy Holmes-Farley]

Not sure what a CO2 scrubber has to do with OP's question.

0.1 dKH only will equate to a drop in Ca of less than 1ppm. You can't measure that with a test kit. Also, your water changes are keeping up with Ca consumption.

Exactly!