Frustrating Salifert dkh readings...

[Tower]

Hi all,

As you may know I was getting some odd readings recently with Ca showing at 500+ so I took a sample to my LFS (Osset) and it came out the same. Fair enough I thought but asked him to check my DKH at the same time.

I had measured it at 9.3 a few days ago but Roy tested with his Salifert and it came out at about 12! :eek:

So... I bought a new Salifert test kit and measured mine again and this time it came out at just over 6!! WTF? I then tested the reference solution which is supposed to be 6.6 +/- 0.3 and it came out at 8!?

I'm really confused here. I've seen a sticky on the chemistry forum on the darkside which shows photos of the various stages of colour and I'm definately doing it right.

Has anyone else experienced this? The date on the new test kit is a couple of years away so not an issue. Has anyone got any advice as it's p*****g me right off. :rolleyes:

Cheers guys... Barry

[moorish]

i have used 2 salifert kits & they both give different readings both kits had good dates but once opened i dont think they have a long shelve life.both mine were nitrate kits one read over 100ppm the other below 50ppm.i think most of these kits are not very accurate & only give you a rough guide.to get a true reading you would have to spend hundreds if not thousands on a proper lab grade meter to check them accurately.derek

[Tower]

Cheers Derek, I'll be bringing the test kit on Sunday to test the reference solution and get a 2nd opinion from you guys.

[TheCoralGardenLtd]

Its true that test kits are only a rough guide, BUT, tbh you should get better results than this. LOTS of factors can play a part in getting accurate readings. Make SURE the test vials are CLEAN before you start, so many people simply tip the old solution out and then re use them, this IS going to give an incorrect reading next time.
Secondly, with the test solution, it IS going to be near enough, (if not contaminated) so, use it and do a test the way you THINK is correct, but VERY slowly drip the reagent in, and stop when you have reached the amount used that is supposed to give you the test value, swirl the sample for a few seconds and look CAREFULLY at the colour! Do this in daylight NOT artificial light!
if you are doing it correctly this should give you a guide to what point to decide the turn point has been reached in real tests.
ALSO, make sure when filling the test syringe that you have the long extension fitted, and that you do NOT suck air in, also that you stop when the BOTTOM of the black rubber plunger is EXACTLY at the line.
If all this is correct, it sounds as if you are doing everything correctly, and the test kit may be corrupt. (usually due to storage in a warm damp fish cupboard!)
Other than this, I can offer no help, throw the kit away and give up, LOL;)
We do about 15 sets of tests a week at the shop, so kits do not last long, and therefore do not generally have a chance to go out of usability, which CAN happen once opend and not used for extended periods.
With doing this amount of tests a week, you kind of get used to what to expect as readings, based on everything else, (they are all linked) and you should NOT just do one specific test and expect it to mean anything!:rolleyes:

[Tower]

Its true that test kits are only a rough guide, BUT, tbh you should get better results than this. LOTS of factors can play a part in getting accurate readings. Make SURE the test vials are CLEAN before you start, so many people simply tip the old solution out and then re use them, this IS going to give an incorrect reading next time.
Secondly, with the test solution, it IS going to be near enough, (if not contaminated) so, use it and do a test the way you THINK is correct, but VERY slowly drip the reagent in, and stop when you have reached the amount used that is supposed to give you the test value, swirl the sample for a few seconds and look CAREFULLY at the colour! Do this in daylight NOT artificial light!
if you are doing it correctly this should give you a guide to what point to decide the turn point has been reached in real tests.
ALSO, make sure when filling the test syringe that you have the long extension fitted, and that you do NOT suck air in, also that you stop when the BOTTOM of the black rubber plunger is EXACTLY at the line.
If all this is correct, it sounds as if you are doing everything correctly, and the test kit may be corrupt. (usually due to storage in a warm damp fish cupboard!)
Other than this, I can offer no help, throw the kit away and give up, LOL;)
We do about 15 sets of tests a week at the shop, so kits do not last long, and therefore do not generally have a chance to go out of usability, which CAN happen once opend and not used for extended periods.
With doing this amount of tests a week, you kind of get used to what to expect as readings, based on everything else, (they are all linked) and you should NOT just do one specific test and expect it to mean anything!:rolleyes:

Stephen,

thanks for the advice. I can honestly say I do all of the above correctly including cleaning vials after tests. I also test PH, Ca, Mg and PO4 using Salifert. This test kit came straight off the LFS shelves and I always do these tests whilst stood next to the window during the day. I tested again this morning and again got 5.8 dkh. I'm going to have a play around at the meet on Sunday and see what happens. I certainly don't want to start ramping the buffer up without being sure as Roy tested and got over 12dkh. :confused:

Cheers... Barry

[Tangman]

Hi Barry what are your eyes telling you m8 is any of your corals dieing are the fish unwell, signs like this is important as this is when you should test. If everything is ok why test and get readings that you cant rely on, the best thing is if you really want to know is find someone with a electronic tester and see what it comes up with. My opinion of test kits is that you can and do get different readings from 2 same make kits, they are only a guide and if you want to be spot on you have to spend £1000s on test equipment. Twiggy :D:D

[TheCoralGardenLtd]

Very strange, it allways confuses me when I get a customer in the shop who is getting one reading, and we, while doing a full test for them get a different one! If this ever happens I immediately get my Manager to double check, and generally he agrees with me. Sometimes we have had the customer bring his kit in, we have used it and got the same result with it as we do with ours, when this happens we have no option but to put it down to customer mis use.
The other thing we have had happen is that customers often read the syringe the wrong way up!:rolleyes:
I CERTAINLY would not start buffering untill you are POSSITIVE you need it! We get more problems with customers using PH buffer than anything else!:D

[Tower]

I CERTAINLY would not start buffering untill you are POSSITIVE you need it! We get more problems with customers using PH buffer than anything else!:D

He He... not something I would do lightly Stephen.

Eric I'm testing because I got cyano when I upgraded to Halides and it's stuck around like a bad cold despite frequent good quality water changes. I'm trying to get my PH up as it's historically been 7.8 (I know this is ok under normal circumstances) but despite running my venturi outside to cut down on Co2 I can barely manage 8.0. I therefore believe that my low PH is linked to my dkh which is why I'm exploring it. I'm just trying to be thorough. :D

Cheers... Barry

[Tangman]

Hi Barry i see what you mean m8, cyno can come with a change of lights. A friend of mine ran T8s and changed to T5s and with hours is tank was covered in Red Cyno, he changed them back and it all went as quick as it came. Twiggy:D:D

[Tower]

That's exactly what happened to me Eric. I syphon as much as I can off when I do water changes but within a couple of days it starts to creep back again.

Something I've not invested in yet is a UV filter as I heard a story about a rep from a VERY big marine equipment manufacturer saying that a small unit just won't make any difference and that only the likes of a 5 stage UV makes any significant impact.

Would a UV help keep cyano at bay at all?

Cheers... Barry

[TheCoralGardenLtd]

As Twiggy says, this is OFTEN a problem when upgrading lighting.:rolleyes:
Cyno will flourish if the status Qou is interupted, just like an algae, it needs two things, nutrients and light, up either and there is llikely to be n un balance, so, when upgrading lights it is paramount to get the water quality as good as possible, and the nutrients as low as you can.
I believe in my opening statement I said test kits were only a guide, you could allways invest in a beter test by someone with the gear to do it, i.e. Tanktest.:cool:

[Tower]

you could allways invest in a beter test by someone with the gear to do it, i.e. Tanktest.:cool:

Stephen, this has captured my interest as I don't know much about it. Do they use lab grade equipment?

Cheers... Barry

[TheCoralGardenLtd]

Apparently yes, not sure if I can mention them on here, as not a sponsor, but can PM a link if required.
Stephen