Calcium/Alkalinity problems

N

nicolebrzu

Member
Hi everyone. I'm about 5 months in to my first salt water tank.
From the beginning I've had an issue with my Calcium being high... usually around 540-560. I FINALLY just bought an alkalinity test because everything I read shows the two tied together. My alkalinity is a little low at 2.28 mEq/L. pH stays a stable 8.2 most of the time.

I'm trying to learn more about these water parameters and some of the articles I have read are difficult to understand. In 5 months I have had very little coraline algae growth. I now have one hard coral which came on a rock I bought for its combination of mushrooms and zoas, so I feel its now very important that I figure this out! That coral has lost most of its color in the two weeks I have had it :(

So... can anyone explain to me the relationship between calcium and alkalinity in more simple terms? How can I raise my alkalinity? I would think that the calcium would lower with use by coral, coraline, etc. but why is my alkalinity low?

Also... can these parameters affect algae growth in any way?
 
C

Clonefarmer

Member
na06003 said:
So... can anyone explain to me the relationship between calcium and alkalinity in more simple terms? How can I raise my alkalinity? I would think that the calcium would lower with use by coral, coraline, etc. but why is my alkalinity low?
Click to expand...
I can't explain the relationship too well, but here is a basic explanation of why the Alkalinity drops faster than Calcium. Both Calcium and Alkalinity are used to make Calcium Carbonate. The ratio used is roughly 20 ppm Calcium to 1 point dkh. Since there is allot more Calcium than Alkalinity, the Alkalinity appears to drop faster.
 
C

cheeks69

Wannabe Guru
RS STAFF
If your not using a two part cal/alk supplement then I suspect the issue is your salt mix. Which test kits are you using ? Have you tested your magnesium levels ? Which salt mix are you using ?
I would suggest you test your freshly mixed salt before adding it to your tank.

Here's more good info:

Understanding Calcium and Alkalinity

 
N

nicolebrzu

Member
Thanks so much for the help!

The test kits I am using are API calcium and Salifert alkalinity/KH. My salt is Coralife. I have not tested mag levels. Would mag also affect calcium and alk?

I am doing a water change today. I will test my fresh mixed before adding to the tank!!!
 
C

Clonefarmer

Member
magnetar68

magnetar68

Member
With the API Calcium test it is important to shake bottle #2 for 10 seconds before using it.

You will need to read those articles to get a better understanding of the relationship between Ca, Mg, and Alkalinity, but the concepts are very simple although rarely are they explained simply.

If you started with normal sea water (or a good salt mix), you will have water with a bunch of stuff in it. Most of it is table salt: Sodium Chloride. But there are many other "ions" in this soup we call sea water. A big one is Calcium. Another big one is Magnesium. There is also a lot of dissolved Carbon Dioxide (CO2) from the atmosphere and other sources. This dissolved CO2 takes a few forms, but the most important for us as reef keepers is Carbonate (CO3) and Bi-Carbonate (HCO3). This makes up the majority of what we call Alkalinity (there are other lesser contributers). Alkalinity trips up a lot of people because we want to think of it as a measure of an amount of stuff in the tank water. The problem is that Alkalinity is only indirectly a measurement of stuff in water. Technically, alkalinity is a measurement of the ability of a solution to neutralize acids. How often do we need to think of something that measures the "ability" of something to do something? So the concept is a little abstract. But here's the main idea:

Corals create their hard skeletons by taking the Calcium and the Carbonate in the water to make Calcium Carbonate (CaCO3)[into the aragonite form of CaCO]. The corals in our tank are therefore constantly removing Ca and Carbonate from the salt water. This removal means the ion soup is changing. As this ion soup changes, so does the chemistry of the salt water. If you take out too much Calcium, corals don't have the raw materials they need to make their hard skeletons. If you take out too much Carbonate (CO3), then they also don't have raw material, but more importantly, the sea water losses it's ability to neutralize acids. Since the decomposing food and fecal matter generates a lot of acids, the pH in the water will start to go down (pH is essentially a measure of acidity). This is deadly for most of the organisms in the tank.

Magnesium's importance is a little more complicated, but Mg is a rather large atom [edit: meant to say Mg2+ is almost as large as Ca2+] that is similar to Ca in some ways. It therefore replaces Ca in some of the chemical reactions going on in the ion soup. There is also a lot more Mg in sea water than Ca, but the main thing Mg does is enable more Ca and CO3 to be in solution than would be there if there was no Mg. This is important because with Mg in the water the corals have more raw material to build there skeletons and sea water can better neutralize acids and maintain a constant pH.

The main idea is to keep these three things in balance. Most recommends keeping Ca around 400-450ppm, Mg around 1300 ppm, and Alkalinity around 8dkH. Here is a good calculator that visually shows the target range for balancing these things in reef tanks: 'Reef Chemistry Calculator FV'
 
Last edited:
N

nicolebrzu

Member
Wow :) That makes a lot more sense. Thanks so much! It is so hard to try to control values when you don't understand why you are trying to control them. Articles make it sound so complicated! You gave a much better explanation! Maybe now when I read the more complicated articles I will have a better idea of what they are talking about...

When I tested my make up water today I found that my salt seems to be the culprit. The new water in the bucket had a calcium reading of 540! Alkalinity was higher than my tank water though. It was around 4.68 mEq/L. pH was low at 7.8.

Should I change the salt I've been using? Is there some sort of buffer I can use? What do you recommend?
 
steved13

steved13

Well-Known Member
PREMIUM
Are you sure your test is accurate. That seems very high for any salt mix, anything is possible but that's very high.

1 other thing if the test kit is accurate... Salt buckets are not homogenous, is it possible you found an area of the bucket where all the calcium is and the rest of the bucket has none? I think this is a long shot also, but just brainstorming.
 
magnetar68

magnetar68

Member
In terms of your specific question about what to do about these values, the first thing you need to do when a value is out of normal range is consider that the test is flawed. This is often user error (not reading the result correctly or doing the test differently than prescribed) but sometimes it's a bad test kit.

In order to keep a reef aquarium in balance, I think you need four kits: Salinity, Calcium, Alkalinity, and Magnesium. Looks like you have two of the four, so that's a good start. For Salinity, it's not really a kit, but an instrument. Personally, I never had any luck with the plastic hydrometers. I could never get the bubbles out or a repeatable measurement, so I bought a $49 Marine Depot refractomer. This instrument is OK and will get you in the ballpark.

Step 1. Make sure you are mixing your salt to the proper salinity. The container might tell you what the Ca, Alk, and Mg should be at this reference salinity. Once you know that is correct, you can address your tank issues. It does not make sense to fix the tank parameters if what is really making it out of whack is the water changes. If your LFS is willing to double check the Ca and Alk in your change water, that might give you some confidence in it. And yes, if your salt is off return it. This is one area I spend more money (although more money does not always mean better salt, in general it does: purer ingredients such as pharma grade cost more for the manufacturer). Also, sometimes our source water is the source of the issues. If you are using tap water or old RO or DI filters, this can be the source of extra ions.

Step 2. You are getting a high Ca reading, so you are not sure if your Calcium kit is right. If you are sure you are following the directions exactly, you can either buy another brand (e.g., Salifert), or take it to your LFS and test their water with it. They should know their value with their kit and you can compare the two. BTW, The API Ca kit is a good brand (I use it), but your particular bottles could be bad for some reason.

Step 3. If your salt mix is OK and your test kit is correct, then somehow your Ca is getting larger, not smaller. If you have been dosing Ca then this is likely the source. If you have not been dosing, then my thinking is that Step 1 or 2 is still an issue.

Normally, reefers will need to dose Ca and Alkalinity. Some get away without dosing Magnesium by using a high quality salt and weekly water changes of sufficient volume. This means they get the Mg they need from the water changes. I have too many obligations for weekly water changes, so I do monthly. This means I need to keep an eye on my Mg and dose it, but I don't need to dose it as much as Ca and Alk.

Step 4. The trick to most major water quality and balance issues is larger (50%) water changes a few weeks in a row -- assuming you are using a good salt that has the proper ionic balance. Either way, between these changes you will need to keep an eye on things. If Ca is low, you need to add it. If it's too high, then don't. The corals will consume it. Same with Alkalinity.

Personally, I use SeaChem Reef Builder for Alkalinity, SeaCHem Reef Advantage Calcium for Ca, and on occasion Reef Advantage Magnesium for Mg. I mix them in my RO/DI top off water a couple of times a week using the beginner instructions and this keeps things in balance. Honestly, the sheer number of products is overwhelming. Until I understood the chemistry, I had no idea what the difference was between them. If used as directed the majority will work to some degree, although there are potential side effects depending on the actual chemicals in a particular product since they add ions in addition to the Ca, CO3, and Mg we want to add. But again, frequent and sufficient water changes can usually keep these things in check.
 
N

nicolebrzu

Member
Thanks for laying it out in parts for me. I do have a refractometer and have tested for calcium and alkalinity. I bought the fourth piece today: a Mg test kit. Mg reading is around 1270.

I will try to test my Calcium test kit against another to see if it is off for some reason.

So my understanding is that I need to be dosing for alkalinity and mag and wait for corals to use up the excess calcium. Correct?
 
bshady

bshady

Member
correct how loaded is your tank with corals? If you dont have many it will take the corals a long time to suck up that much calcium. What salt did you swith too? In the past i have tried many salts such as instant ocean, seachem marine salt, red sea, seachem regular salt, and had previous problems with my calcium being over 500 ppm. I changed to reef crystals and have had less problems with phosphates and no problems with calcium.
 
magnetar68

magnetar68

Member
At 1270 you won't need to dose too much Mg, so keep a close eye on it. But yes, no need to dose Ca since it is already high and the corals will bring it down. You definitely want to dose Alkalinity since 2.28 mEq/L is low, especially for that high of Ca. A better number for Alk (assuming you want to get Ca down to about 420ppm) is about 2.86mEq/L (8dKh). But don't try to do it all at once. I would dose a few times a week and slowly raise it up.

BTW, how big is your tank and what are you using to dose Alk?
 
Boomer

Boomer

Reef Sanctuary's Mr. Wizard
magnetar68

Very nice posts and very well done:thumber:

A couple of notes:

If you take out too much Carbonate (CO3), then they also don't have raw material, but more importantly, the sea water losses it's ability to neutralize acids

It is actually to much HCO3-. Corals and most marine plants of all kinds use HCO3- for both their carbonate and CO2 needs by conversion. HCO3 - makes up almost 90 % of the Alk in seawater and CO3-- only 8 %

Alkalinity since 2.28 mEq/L is low


Yes, we often call that low for reef tanks but that it for actual reefs.

420ppm is about 2.86mEq/L (8dKh)

More like 2.95 meq/l


Nice to have you here hope you stick around :D
 
magnetar68

magnetar68

Member
Thanks Boomer! Yes, I knew when I wrote that I was speaking about "Carbonate" as the combined amount of CO3 and HCO3 but not being clear; and I was not sure which was the greater contributor. I was thinking someone would call me out on it, but I did not want to over complicate the story. Thanks for keeping me honest.

I meant to say that 2.28mEq/L was low relative to a Ca level of 540-560ppm (i.e., its not in balance).

I used the following source for the conversion, looks like it is a little off? OZ REEF - Alkalinity Conversion
 
Boomer

Boomer

Reef Sanctuary's Mr. Wizard
No, Raymo you conversion is not off. It is @420 ppm Ca++ the balance is 2.95 meq/l not 2.86 meq/l

and I was not sure which was the greater contributor.

Something to remember is pH. As the pH rises there is less H+ (H3O) in the water. So, at a pH of 8 there is less H to form less HCO3- than there is at a pH of say 7.5, where there is more H* to give more HCO3-. These are also controlled buy temperature and Salinity. As Temp rises at the same pH there is and decrease of the HCO3- and increase of CO3--. So, for example, at 20 C there will be about 5 % more HCO3- than at 30 C and 5% more CO3-- at 30 C vs 20C. And as salinity drops there is more HCO3- at the same pH. Lastly, if Alk increases keeping the same pH, there will more CO2, more Alk but the ratios of Alk ( HCO3- vs CO3--) remain the same, there is just more of it /Alk. This is why two tanks can have the same pH but different Alk's, where there is more CO2 in the higher Alk tank. If two tanks have the same pH and Alk both have the same amount of CO2. Also, as pH rises there is less CO2, also a function of Temp and Salinity.

Forgot

We start at 360 ppm Ca++ and for each 20 ppm rise above that 360 is 1 meq/l ( 2.8dK)

420 - 360 = 60 / 20 = ~ 3 meq l
 
You must log in or register to reply here.
Top