Help with calcium test

[calihawker]

Hi
I'm trying to get some insight and help with variuos testing kits for calcium. I've had my tank up and running for 6 months or so and I have not been able to get results that I can trust with regards to calcium. My PH and Alk. are good and stable so I'm not overly concerned about the well being of the tank but I would like to know with some conviction what my calcium levels are.

I've been testing with a Seatest kit primarily and although I've made changes with kalkwasser and a calcium reactor I've never EVER had a calcium reading other than 360ppm. I bought a Salifert kit and this morning I tested with it and the results were off the charts! I could not get it to turn blue! So I grabbed the Seatest kit again and guess what? 360ppm. I did both tests twice with the same results.

Do you have a favorite kit? Are there major differences between kits?

Thanks for any help.
Steve

[Randy Holmes-Farley]

When using the Salifert kit you can add more syringes of fluid as necessary. Just add the values for each syring together. That will give you an actual value, and we can compare the kits. You'll likely get the color change during the second syringe.

Also, be sure that you are using the specified amount of tank water. :)

[calihawker]

Thanks
I'm very careful with my testing procedures. I'm just confused why I would get drastically different results between kits. If I start adding a second syringe, the Salifert kit is saying my calcium levels are over 500 ppm.

Steve

[Randy Holmes-Farley]

Yes, it would mean that the Salifert kit is reading over 500 ppm, and that one or both of the kits must be in error. That's not especially uncommon, FWIW.

[Habib]

Steve:

Did you use the volume of water as mentioned in the instructions?

The old version salifert uses a 5 ml syringe but you have to use 3 ml. So certainly not a full syringe.

The new version uses a 2 ml syringe and you have to use with that one the full syringe (2 ml).

The new version has been done in that way to avoid the mistake which sometimes was made by taking more volume of water than required for a correct value. :)

[MSHUR]

hi,habib
i have similar problem...i have lots of ca bild ups on my sponge.
i use rowa reactor and that sponge on top gets cloged with ca.
using salifert kit and i only have 400-410.
regards,mike

[Randy Holmes-Farley]

A few folks do seem to get precipitation of CaCO3 when using certain iron-based phosphate binders. I've not seen a good explanation of why yet.

Perhaps tiny bits of Fe(OH)3/Fe2O3 break off and act as nucleation sites for CaCO3 precipitation.

Any ideas, Habib?


Here's a thread where it is discussed:

http://archive.reefcentral.com/forums/showthread.php?s=&threadid=380764

[Habib]

Randy:

Thanks for the link. :) I had not seen it yet.

I'll go through it ASAP.

FWIW I have not seen or heard of such problems with our Phosphate Killer. In some comparsion tests quite a while ago I was surprised to note that the Rowaphos had become like a brick while under the same conditions no clumping was observed with our product.

[Randy Holmes-Farley]

This is reaching quite a bit, but suppose that:

1. Those aquaria that get such precipitation are actually in a supersaturated state (with respect to CaCO3) that is being held back from precipitation by organics, magnesium, and phosphate that is poisoning the crystal surfaces when they form.

In general this is true for nearly all reef aquaria, but these may be especially dependent on phosphate levels to prevent abiotic precipitation, or may have unusually high supersaturation (high pH, calcium, and alkalinity).

2. Then when using a phosphate binding material, the downstream area is depleted in phospahte, so the liklihood of precipitation of CaCO3 rises, and in some cases, it is actually substantial.

[Habib]

2. Then when using a phosphate binding material, the downstream area is depleted in phospahte, so the liklihood of precipitation of CaCO3 rises, and in some cases, it is actually substantial.


IMO only if the kinetics of seed formation and crystal growth are much faster than the average residence time in the canister with the media.

Since the kinetics , even in absence of things like PO4 but with the presence of Mg, are slow I would consider it not so likely.

What do you think about it, Randy? :)

[Mimbler1]

For the substantial drops in Ca and alk reported, it would have to be more than a local abiotic precipitation - although it might be greater locally and more easily noticed. Randy's theory sounds plausible, and anecdotally, I have not suffered this problem, and I had low PO4 before RP, so it would probably not have been limiting for abiotic precipitation.
Mike

[Randy Holmes-Farley]

IMO only if the kinetics of seed formation and crystal growth are much faster than the average residence time in the canister with the media.

Since the kinetics, even in absence of things like PO4 but with the presence of Mg, are slow I would consider it not so likely.

I agree with that if we were talking about precipitation on particles that passed through the reactor (or bed). Snowstorm types events.

But if we are talking about locations permanently inside the reactor (like on the iron oxide particles themselves) or in the downstream plume from the reactor (like a sponge near the outlet), then I disagree. Those areas are permanently in the low phosphate water, and might be more likely to continue precipitation.

FWIW, this idea would relate to organics (such as organic phosphates and carboxylates) that would be bound to the iron oxide, but which also bind to CaCO3 and help prevent precipitation. So the different results that folks see might relate to organic levels as well as phosphate levels (and, of course, the supersaturation of CaCO3).

For the substantial drops in Ca and alk reported, it would have to be more than a local abiotic precipitation - although it might be greater locally and more easily noticed.

What size of drop have you seen?

[Mimbler1]

"For the substantial drops in Ca and alk reported, it would have to be more than a local abiotic precipitation - although it might be greater locally and more easily noticed.

What size of drop have you seen?"
Randy,
In my system I have seen zero drops of Ca and alk with RP use, but others have reported significant calc and alk drops with RP use.
regards, Mike

[Randy Holmes-Farley]

OK. :)

[Habib]

But if we are talking about locations permanently inside the reactor (like on the iron oxide particles themselves) or in the downstream plume from the reactor (like a sponge near the outlet), then I disagree. Those areas are permanently in the low phosphate water, and might be more likely to continue precipitation.


Yes but there is flow so the residence time is short.

This will not be true if the calcium carbonate seeds would adhere to something in the low PO4 regions. In that case the residence time will be high and long enough for further growth of the seeds.

Perhaps the presence of the calcium carbonate precipitate demonstrates the ability of calcium carbonate to adhere on some of the surfaces in the reactor. So seeds could adhere as well.


The clumping I have seen with Rowaphos has a totally different nature.

There are then perhaps various reasons for clumping to occur or not.

The same is probably true for the calcium carbonate formation some people are mentioning.