Calcium Conundrum

[Bore-Punch]

My tank is testing over 1000+ ppm Ca++, is this possible and if so whats the solution to lower it?

first off tanks specs. 270 gallon system running with a closed loop pump. No filtration. (my reeflo return pump is being repaired atm) system finished a 40 day cycle a month ago and i have 1 blenny 8 chromis and a sailfin tang. 40lbs of fiji live rock and about 120lbs of BRS pukani and 40lbs marco dry rock, 3.5inch sandbed using marco rocks sand 50% coarse on the bottom, 50% fine ontop. seeded with 10lbs of garf grunge. I have only done 1 30% water change since starting the cycle.

Testing is done with a lamotte smart 3 colorimeter
parameters.
temp 79 deg F
salinity 1.025 sg
ph 8.19
ammonia 0.00 ppm
nitrites 0.00 ppm
copper 0.00 ppm
phosphates 0.32 ppm
nitrates 7.39 ppm
silica 11.65 ppm

alk tested with lamotte titration
192 ppm - 10.752 DKh - 3.84 meq/L

Oxygen with salfert test
7.0 ppm

Calcium with lamotte total hardness titration
1362 ppm !
now on this test i got it to turn blue at 557ppm but after a settling for 20 seconds it would go back to purple....it wasnt until 1362ppm that it would stay blue (endpoint)

well this test is cumbersome to use so i decided to try another test kit to verify.

API Ca Test kit
turned purple at 520ppm
could not get it to change from purple to blue ...i stopped at 50 drops which is equivalent to 1000ppm Ca


tried the above test twice with the same results

whats going on here.....i use IO salt do i have a bad batch? am i interpreting the endpoints wrong? possibly an interference that is choking the endpoint after the intial color change?

also i know my nitrates phosphates and silica are way high and i have the dinos to prove it but the lawnmower blenny is loving it....just waiting for the pump to get back here so i can start running the skimmer, ozone, gac, and gfo.

 

[Randy Holmes-Farley]

The Lamotte is probably reading in ppm calcium carbonate equivalents, and 1000 ppm calcium carbonate equivalents = 400 ppm calcium ion.

 

[Bore-Punch]

all those #s are after the corrections... so it turned blue first at 108 ppm titrate but i need to multiply that by 12.9 because its really meant for fresh water so thats the salt water correction...and i diluted it as per the instructions and verified that i used RO/DI at 0ppm TDS to do the dilution. so that equates too 1393.2 CaCO3 multiply that by 0.4 i got 557ppm Ca .... and i did the same math for when the test finally stayed blue and was at 1362ppm Ca not CaCO3... :/ as i said its not the most user friendly test which is why i verified with another test kit. any thoughts randy?

 

[Randy Holmes-Farley]

Can you explain exactly which Lamotte smart 3 colorimeter method? Are you sure it is not also detecting magnesium as hardness?

Forget the test turning blue. Not sure what that is but the endpoint of a calcium test follows quickly after it turns purple if this is pink dye to start with.

557 ppm is not especially unusual, although I doubt that IO is that high. If you added nothing, either the salinity is higher than you think, or it is in error. Some other salt mixes start that high.

Am i missing something else?

 

[Bore-Punch]

the alk and calcium tests are titrations and not used through the smart 3 colorimeter. the total hardness test does both calcium and magnesium, but to get the magnesium value you have to subtract the calcium titration from the total hardness titration. My total hardness titration worked fine and i measured 7379ppm CaCO3 subtracting the results from when the Ca titration from where it first turned blue and after all the corrections i had Ca = 557ppm and Mag = 1437ppm, however doing it with the Ca results where it stayed blue the results are 1362ppm Ca and 954ppm Mag

So ya i guess my question is why would it take twice as much titrate to make the endpoint stay blue....note that the API test essentialy did the same thing...turned purple which means your 2 drops or 40ppm away from it reaching its endpoint....but it wouldnt reach it even after double the titrate added.

it is possible that my salinity is higher than im reading...im using a simple IO hydrometer which is prone to error....but i cant imagine it would be off that significantly...

 

[Bore-Punch]

http://www.lamotte.com/images/pdfs/instructions/4824drlt.pdf

instructions for the total hardness titration.

 

[Bore-Punch]

double post :/

 

[Bore-Punch]

so after 2 hours i just went back to look at the API test tube where i stopped at 1000ppm worth of titrant after it still hadnt turned blue ....now , of course , its blue....so is my problem a patience thing....after the initial color change do i need to add just a bit more then let it sit for 15 minutes to let it all combine.....maybe?

 

[Bore-Punch]

also my ph was lower during the cycle ...7.79 ph ...is it possible some of the rock and sand dissolved into the water. That should also have brought Alk way up ....im stretching here because im out of ideas....i may redo the tests latter tonight and let the samples sit longer after the 1st color changes

 

[Rybren]

I use the API Calcium test. It turns dark blue within two drops of it turning a dark purple. There's no waiting - it is immediate - but ONLY if you swirl/shake the tube. If you don't, then only the upper portion of the solution will be blueish.

 

[Bore-Punch]

i shook after every drop as per the instructions....there may be an interference in the water that is affecting both titrations?....high silicates?

also when i put the drop in the very top of the tube is blue..then i mix it and its all purple again....and this continued all the way to 50 drops (1000ppm Ca)...then i gave up :/

 

[disc1]

The indicator in a calcium kit doesn't react to calcium. It requires a sensitizer, usually magnesium in the lab but since seawater contains so much magnesium I would reckon they probably use zinc.

Anyways. When the calcium is all used up, the next drop of titrant will not have any calcium to react with and will instead go take the zinc from the indicator changing it's color. So technically speaking, the end point is the drop before it changed color. By keeping the dye concentrations right, they can make the color change really fast and you can just go by when it turns blue. If the dye or the sensitizer gets a little too much, then you're going to end up with a purple color while you continue to titrate the sensitizer instead of calcium. This leads you to a deceptively high result, although 1000ppm (if it's not CaCO3 eq like Randy said) is a bit much.

Long story short, with a pink / blue calcium test, you're not looking for blue. You're looking for something that's not the original pink anymore. If you see purple, you're done.

 

[Randy Holmes-Farley]

I agree. If you want to use these kits, go with the 557 ppm value. That still seems likely to be off in these circumstances using normal IO and not a lot of other supplements, however.

 

[Bore-Punch]

Thanks for the input guys, im going to redo the tests tonight with that in mind, maybe its time for a refractometer as well to verify my salinty. Thanks again for the help.

 

[incognitus]

The indicator in a calcium kit doesn't react to calcium

That´s not true.

Indicator is murexida which is red attached to calcium and blue when free. In the middle there is a mixed of colours and maybe hard for someone to realize there is not red color.

 

[disc1]

That´s not true.

Indicator is murexida which is red attached to calcium and blue when free. In the middle there is a mixed of colours and maybe hard for someone to realize there is not red color.

In that case, the color is pH dependent.

I was under the impression that many kits were using zincon, or a derivative thereof. I'm just judging from the colors, but it looks like the right thing.

It would be far better to use an indirect indicator. If they aren't then they should be.

 

[Randy Holmes-Farley]

duplicate

 

[Randy Holmes-Farley]

FWIW, the Hach kit uses Hydroxy Naphthol Blue.

 

[Habib]

It sounds like a sluggish end point.
I suspect that there is a significant amount of precipitated calcium in your water,causing the sluggishness and a false high value. Or the magnesium is not precipitated nicely/correctly with the reagents causing release of magnesium after the initial end point.

 

[disc1]

FWIW, the Hach kit uses Hydroxy Naphthol Blue.

OK, so that's a direct indicator. I rescind portions of my previous response.

Still, if you hit a purple then the next drop or at most two should put you over the line. If it doesn't then you've got something going wrong.


Where's Habib when you need him?