Question about hardness test

[Lenny]

Hi,

I got Ben's test kit at the end of last season and just started using it. It's all a bit overwhelming at first, but after several uses most of it is becoming second nature already.

One question I have is about the hardness test. My hardness is around 330 right now. Unlike the Alkalinity test, which has a distinct and immediate color change, the hardness test seems to transition from red to blue more slowly (sometimes it really seems redish blue to me for a few drops).

Do you generally record the value when the color is no longer distinctly red or do you keep adding drops until the color is distinctly blue?

Thanks,
Lenny

[Watermom]

When you get to the point of it not being red, it starts to get purplish. I continue adding drops. At some point, one drop will change it to a distinctively blue color. That is what I record.

Watermom

[duraleigh]

Hi, Lenny,

Yeah, mine does the same. I think the essential element to remember is you have a wide latitude of acceptability. So a reading of 310-350 would be close enough for our purposes.

I record mine when it clears all the way up just so I'll have consistent readings each time. I think as long as you do the same thing each time you're good to go.

(About five years ago, I enjoyed a spectacular meal at an upscale seafood restaurant in downtown Wilmington. It was in the middle of downtown and right beside a multi-level parking deck. Does that ring a bell? Is it still there?)

Dave S.

[waterbear]

Hi,

I got Ben's test kit at the end of last season and just started using it. It's all a bit overwhelming at first, but after several uses most of it is becoming second nature already.

One question I have is about the hardness test. My hardness is around 330 right now. Unlike the Alkalinity test, which has a distinct and immediate color change, the hardness test seems to transition from red to blue more slowly (sometimes it really seems redish blue to me for a few drops).

I can answer this question. I have kept saltwater/reef aquariams for close to 30 years now and the calcium hardness test is a standard one for saltwater so I am familiar with the chemistry involved. If there are other metals present (copper is a main problem but other metals can affect it) your endpoint will turn purplish and not a distinct change to blue. You might even notice what seems like purple particles suspended in the liquid. The anser is to add about 5 or 6 drops of the EDTA (reagent #3 in Ben's or Taylor's kits) FIRST before you put reagent #1 in your test sample. This will bind up the metals. When your do your titration count those drops! (for example, you add 5 drops first and then your titration takes another 15 drops = 20 drops total which is 200 ppm calcium hardness)

Do you generally record the value when the color is no longer distinctly red or do you keep adding drops until the color is distinctly blue?

The proper way to do the test is to add a drop of titrant, swirl the tube for about 30 seconds and see if the endpoint is a distinct blue. It is a bit time consuming but is the most accurate way. If you do this you will find that the purplish colors you see will not hold. The accuracy needed for a fishtank is proably not necessary for a pool but do swirl for at least 10 seconds between drops! You will finally reach a point where one more drop causes a change to a blue color that is unmistakable! It is easier to see the color change in the shade rather than in direct sunlight also.



Thanks,
Lenny

Hope this info has been helpful!

[CarlD]

I can answer this question. I have kept saltwater/reef aquariams for close to 30 years now and the calcium hardness test is a standard one for saltwater so I am familiar with the chemistry involved. If there are other metals present (copper is a main problem but other metals can affect it) your endpoint will turn purplish and not a distinct change to blue. You might even notice what seems like purple particles suspended in the liquid. The anser is to add about 5 or 6 drops of the EDTA (reagent #3 in Ben's or Taylor's kits) FIRST before you put reagent #1 in your test sample. This will bind up the metals. When your do your titration count those drops! (for example, you add 5 drops first and then your titration takes another 15 drops = 20 drops total which is 200 ppm calcium hardness)

Wow! Can anyone else verify this??? If so, we should include it as part of the CH test!

I AM impressed!

[mwsmith2]

This is something that was discussed before. Ben said it's coming from Magnesium in the water which is screwing with the results. I've tried the pre-titrate method and found that......

....it didn't make a difference!

I used to have a marine aquarium too, and I still have my LaMotte lab-grade test kits. They do the same thing. It's just the nature of the beast.

Michael

[waterbear]

It's worked for me. My understanding is any bivalent postive ion can effect the results but I could be wrong on that. Gave up on LaMotte for aquariums years ago. Too Pricy! there are kits with as much accuracy for less money.

[CarlD]

My older son has gotten in keeping fish over the last year. He kept his first fish, a betta named "Ridely" alive for 6 months, changing the water religiously. So now he has a 20 gallon aquarium with mollys and plattys--and the latter keep having babies--and guess who gets stuck testing the water--the guy who knows how to test pools! I was gonna name the fish "Maki", "Nigiri", "Sashimi" and "Sushi" but he really did NOT appreciate that. But with "Mercury" getting pregnant alot, 4 fish is now 8 fish....

[waterbear]

This is something that was discussed before. Ben said it's coming from Magnesium in the water which is screwing with the results. I've tried the pre-titrate method and found that......

....it didn't make a difference!

I used to have a marine aquarium too, and I still have my LaMotte lab-grade test kits. They do the same thing. It's just the nature of the beast.

Michael

I pulled out my Taylor manual today and it confirmed what I said about Iron or Copper being the culprit. Here is the quote:

"This usually occurs due to small concentrations of iron or copper in the pool water that cause the test to develop a purple color rather than blue. To alleviate this, add five or six drops of the titrant (hardness reagent) to the water sample first and then conduct the tests as usual. the titrant 'ties up' the interfereing soluble metals and the test can be completed with a distince endpoint."

Reagent #1 (sodium hydroxide) is added to the sample to remove the interference from the magnesium.

Btw, the calcium test kit I use for my aquariums now is NaturReef. Much less expensive than LaMotte and just as accurate, althought I'm sure Ben's or Taylor's would work just as well. Think I will try it out and compare results for a few weeks and see. I've use my SeaTEST phosphate kit to double check the reading the pool store gave me on phospates and it was a perfect match.

[mwsmith2]

Mmmmmmk. Only thing is, I've been tested for both Fe and Cu, both showed negative. I still get the funky clumping and semi-solid colorchange. I'm not sure if that's the only thing at work here? *shrug*

Michael