Calcium Levels Disagreement

[ReeFish]

Longish-time member, first post!

After more than a year researching and reading, I have set up my own nanocube 12G aquarium. I am a molecular biologist by trade and had freshwater for 14 years.

The problem: my two calcium test kits are showing very different results. My Tropic Marin test kit shows <300ppm, while my Red Sea test kit shows ~400ppm. Which one is right?

I'm using Tropic Marin Salt Mix, which I've already read has low calcium issues. I've been dosing 10ml calcium carbonate for two days and the Red Sea went up from <300ppm to 400ppm, but the Tropic Marin is still not registering anything. My gut instinct, as scientist, is to trust the Tropic Marin test kit, though I don't know the chemistry either kit is using.

I read a lot of opinions about all the test kits out there, and I guess I am asking for opinions here, but please don't respond with: "Blank Stinks!" If you have a reason to trust one company's kit over the other, please let me know!

Today's readings: Temp: 77.9, pH 8.2, Spec grav 1.022, dKH 8.5, Ammonia: 0ppm, Nitrite: 0, Nitrate: 0, phosphate: 0.2mg/l, calc - see above.

 

[azgard1]

I'll be watching this thread. I expect your response will be something like La mote or Hatch for absolute values. They are quite expensive. I currently use Aquarium pharm, but I also wonder as my La mote seems to show higher levels, but could be it's older reagents. Don't really know the life of typical reagents. Boomer I'm sure will respond. But other than the pro lab kits I wonder what is the leading consumer kit with some amount of reliability?

 

[dnjan]

First, I use salifert test kits for almost everything. Good accuracy, and not too expensive.

Second - I assume you are adding calcium chloride, not calcium carbonate (calcium carbonate has very low solubility at normal saltwater pH). Adding calcium chloride long-term is not a good idea unless you do frequent water changes. Adding calcium chloride for a long time will skew the chloride ion content. Better to add calcium hydroxide (disolved in water - "kalkwasser") or use a calcium reactor, which disolves solid calcium carbonate using lowered pH.

 

[ReeFish]

Dnjan - I apologize:exclaim:, I am using Calcium chloride. I'm not concerned about the chlorine ions as I perform a 10% water change every week and because I will be switching to a salt mix that has higher levels of calcium shortly.

 

[Kurt_Nelson]

Will also chime in with a pitch for either API (Aquarium Pharmaceuticals) or Salifert for calcium. I use both and they normally agree with each within 20ppm, depending on how you read the color of the last "drop" on the API test. I'd take the levels given by the Salifert test as Gospel.

 

[ReeFish]

I realized something with the Tropic Marin test. The test is fairly complicated three part titration system. The addition of two of the reagents uses syringes with pipette tips. The volumes used are small enough that the extra volume contained in the pipette tips adds an additional 20% or more to the sample. This is obviously a very serious problem and I corrected it, which lead to a much more reasonable reading of 350ppm (before it wasn't even registering). However, my Red Sea kit is now showing 450ppm, so there is still a significant discrepancy. What method does the Salifert system use?

 

[91YOTA]

salifert ca test uses 3 reagents also (1 powder and 2 liquid) the scale ans results adjust for the air volume added by the pipette also.... ime its very easy to use

 

[Kurt_Nelson]

The Salifert test doesn't really "adjust" for the air volume. All you're measuring is how much of the last liquid you're putting in. If you suck up solution into the syringe until the plunger is at 100ml, and then read where the plunger is at when you're done pushing solution out of the syringe, the difference between the two readings is how much fluid you pushed out - regardless of how much air was in the syringe. And that amount is what is important.

 

[jimw369]

Might want to head to your nearest LFS and get them to check it with their kit. Might be interesting to see what test theres is closest to.

 

[ReeFish]

My LFS uses Tropic Marin to test and received the same results as my Tropic Marin kit. So at least I know my kit's probably not bum, and the expiry on it is 05/11, so it should be good. I think it uses the same chemistry as the Salifert test uses, from what you all are describing. I'm going to trust its readings for now, and not Red Sea's readings. The other thing I was considering is getting a calcium probe, but the expense... Thanks for everyone's input!

 

[jimw369]

My LFS uses Tropic Marin to test and received the same results as my Tropic Marin kit. So at least I know my kit's probably not bum, and the expiry on it is 05/11, so it should be good. I think it uses the same chemistry as the Salifert test uses, from what you all are describing. I'm going to trust its readings for now, and not Red Sea's readings. The other thing I was considering is getting a calcium probe, but the expense... Thanks for everyone's input!

Yeah, "but the expense", welcome to saltwater.

 

[Boomer]

Late but

Red Sea's = Crap

calcium probe = Can be really finaky

API = Good and usually the Salifert.

If you want the real deal in a kit, as best you can, then get a HACH Digital Titrator if you have $200 floating around loose :lol:

 

[chris&barb]

no one mentioned that your SG is low. if you raise it up to NSW levels 1.026 you will have a higher Ca level.

and as another poster said you dont need to adjust for the volume of reagent in the tip. just pull back the plunger to where you are supposed to and take your final reading at the position of the plunger. you could put 10' of air line hose on the syringe and if you pull it back to 1ml that's all your going to get

 

[ReeFish]

Thank you to everyone for your opinions and experienced advice! I will move to API or Salifert. Also, I did increase my SG after getting a refractometer and the calcium did improve - I just forgot to mention that. You are also all very correct about reading the syringes with pipette tips attached. Sometimes I can be a little dim Thank you again!