# Testing for Calcium



## Grobbins48 (Oct 16, 2017)

I have looked through my water quality report and it does not list anywhere thr Ca ppm. How are people getting this reading? The only test kits I see are for saltwater.

On the same note, how would one test for Mg? Or do you use Gh test combined with some Ca test and do some math? 

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## Immortal1 (Feb 18, 2015)

@Grobbins48 best info I can offer is what I have been doing lately.
Get an API CA test kit. This kit is definitely designed for the salt water crowd but can be useful for us with a little modification.
First, find a container that will hold a little more than 10ml. Get a 10ml sample of tank water and add 20 drops of bottle 1 (10 drops in 5ml is normal). Now, each drop of bottle 2 roughly equals 10ppm calcium.

Once you get a good reading (takes a bit of practice / good observation to see color change), now you need to test the GH of your tank water. More or less, GH is made up of CA and MG.

So, 10ppm CA is equal to 1.4 dGH. In my case, I have a CA reading of 50ppm or 1.4 * 5 = 7dGH. My tank GH equals 11dGH. So, 11 - 7 equals 4dGH.
That means of the 11 dGH total, CA makes up 7dGH and MG makes up 4dGH.

MG equals 0.23dGH per 1ppm. So, 4dGH/0.23 equals 17.4ppm MG

Hope this helps


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## Deanna (Feb 15, 2017)

I had great difficulty trying to make the API kit work. I found that the Elos Aqua Calcium Test Kit (Amazon) is much easier.

For magnesium, I use the JBL kit from Germany (JBL Mg Magnesium Test Set Freshwater). I got it via Ebay from one of several British sellers. Make sure you get the FW version and not the SW version.


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## Surf (Jun 13, 2017)

> I have looked through my water quality report and it does not list anywhere thr Ca ppm. How are people getting this reading?


While your utility doesn't list it many other do. My impression is that most are not using calcium test kits.


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## macek.g (Sep 4, 2013)

Examples for fresh water


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## Edward (Apr 11, 2005)

API Ca test kit can detect 0, 5, 10, 15, 20, … ppm Ca. 

Get 20 ml of aquarium water, add 5 drops of #1 solution and mix.
Start adding 1 drop of #2 solution and mix and watch for colour change from pink to blue. Each drop of #2 solution equals to 5 ppm Ca. 

*How do I test for Mg?*
First test for GH and Ca, then calculate Mg.
Mg testing
((17.86 x dGH) - (2.5 x Ca ppm)) / 4.1 = Mg ppm
(ppm dGH - (2.5 x Ca ppm)) /4.1 = Mg ppm


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## Grobbins48 (Oct 16, 2017)

So the API marine will work, just with a diluted (10-20 ml) as my scale? The math and all that is fine, and I understand. I just was not sure on the reliability of API Ca test for freshwater.

FWIW, my Gh is 8 right now, which is why I want to know my ppm.

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Okay, now I understand why it is a saltwater kit. One drop is 20mg/L, so using a larger ratio of water to solution yields a finer scale. Ie. 20ml of water. Thanks for the advice everyone.

I guess the question comes, with a gh of 8, does it matter? I mean to really hone in on things I suppose. I might just grab the test anyways to have and know!

Thanks again for the help and hopefully this helps someone else out too. 

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## Immortal1 (Feb 18, 2015)

I guess to answer your question @Grobbins48 "does it really matter" - sometimes!
Your 8dGH, depending on your water source, could be 80-90% calcium with very little magnesium. This would result in a Mg deficiency that would show up in the plants, but could also limit uptake of other macros/micros.
Not a hard/fast rule, but a Ca:Mg ration of 3:1 to 4:1 seems to work for most. When it was pointed out to me that I was having a Mg deficiency I thought "no way, I'm at 11dGH". Well turns out my tap water was high enough in calcium that my Ca:Mg ratio was about 6.5:1. I have since corrected this and have been steady at 2.8:1 to 3.5:1 - plants seem much happier.

FYI, look at post 139 in this thread Joe's tap water is 8.75:1 to 10:1 Ca:Mg


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## Grobbins48 (Oct 16, 2017)

Ah wow that is interesting. Funny enough when I started dry dosing, I ordered Mg, and dosed at EI levels. I guess part of me thought that our water here was lacking- with absolutely no scientific backup! HA!

I just ordered the API test kit from Amazon, so I'll post results when it comes in. Good info on the ratios, I'll keep reading on that topic.

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## diverjoe (Oct 21, 2016)

Recently been watching a bunch of YouTube’s on calcium and magnesium titration tests. It has been enlightening to say the least. Seems there is a whole lot of 1st year chemistry out there that applies directly to what we are all doing lol. The dance that occurs between these basic chemicals of life is pretty humbling in its simple complexity. I just got a salifert magnesium. And a seachem iron. I have been fight omg algae with sick plants and I have a suspicion that it is the lack of mg that is causing the carbonates to be sucked up and lost to something like calcium carbonate. At any rate a little hard science backed data front the test should tell a tale. Oh and also take a look at Dennis Wongs website advancedplantedtanks.something. Just found it last week it has really cleanly explained documents and videos about all of this. 

Cheers


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## Grobbins48 (Oct 16, 2017)

Kit came in today, but I'm reading some conflicting info. To get a higher resolution, I understand adding more water, ie. 10ml. Would I not want to then keep bottle 1 at 10 drops, making every drop of bottle two equal 10ppm. Or to get a 5ppm resolution, use 20ml of water and still 10 drops of solution 1?

I might be missing something but it seems the titration should be the reaction of bottle 1 and bottle 2 due to the Ca concentration in the water. With a diluted solution it would take more drops to get the reaction, thus a finer redolution.

Thoughts?

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Okay so I tested the tap a few ways:

1- The normal 5ml test with 10 drops solution 1 (normal saltwater test). I got to the 2nd drop of bottle 2 and water went from pink to blue. This would indicate ~40ppm, low resolution of 20ppm.

2- Did the test with 5ml of water and 5 drops of solution 1. Again, it only took two drops to get to blue. So does this mean 20ppm, or is the test flawed? not sure how I feel about this test

3- Did the test with 10ml of water, and all 10 drops of solution 1. It took 4 drops of solution 2 to change from pink to blue, so this would indicate ~40ppm Ca, with a resolution of 10ppm.

So with the assumption right now (I know, assumption... yikes...) that I have 40ppm Ca, I tested tap GH, where I got 8 drops. Plug these two numbers into the Mg formula and I get:

(17.86*8)-(2.5*40)/4.1 or (142.88-100)/4.1 which equals 10.46ppm Mg. This makes the ratio roughly 4:1, so not too far off, but could continue to dose Mg at 1/2 EI levels it seems to add ~7ppm Mg/ week.

Thoughts on this method? Am I going about this with the right idea, or way off base?


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## Edward (Apr 11, 2005)

The API Ca test kit was designed for reef keeping with 400 ppm Ca levels in 5 ml, 10 drops #1, 20 drops #2.

For freshwater planted aquariums we need 20 ppm Ca, 20 x lower.
1 drop #2 in 5 ml, 20 ppm resolution
2 drops #2 in 10 ml, 10 ppm resolution
4 drops #2 in 20 ml, 5 ppm resolution

So when we pick the best 5 ppm resolution then it takes 4 drops of #2. By changing #1 from 10 drops to 5 drops, we are doubling the test kit value otherwise it runs dry. I have verified it with Ca solutions to be sure.


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## Grobbins48 (Oct 16, 2017)

Okay thanks for helping to clear that up for me. So for our use, solution 1 at 5 or 10 drops yields the same results. What gives me resolution is increasing the sample size of the water by a factor. 

So 20ml of water, 5 drops solution 1, will give us a resolution of 5ppm for each drop of solution 2.

I'll do the test again with the description above and see what results I get. 

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Test completed, results are in. Using the 20ml of water, 5 drops solution 1, I added 8 total drops of solution 2 in order to turn blue. That would give me 5ppm * 8 drops = 40ppm. 

So I guess validated a few ways, I am fairly confident my tap is at ~40ppm Ca right now, which by the math gives me the ~10ppm Mg. 

Unless anyone can advise otherwise, I'll probably add ~7ppm of Mg weekly, as I am EI dosing on my tank.

I appreciate everyone's advice and help with this one!

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