PDA

View Full Version : Alk test confusion - Need some help


advancebc29
08/27/2012, 07:23 AM
So I have been using salifert to test my alk for at least the past 1.5 years. My test kit was just about empty so I ordered one of the RedSea Pro Alk test kits. Now this is where I became puzzled.

Correct me if I am wrong. On the sailfert test after reaching my color change I read the amount left and correlate that to the chart? In this case I am sitting at .52 ml left which is about 7.7 dkh (doing this from memory so could be off to what the exact dkh is). Not subtracting from 1 ML ?

Using the RedSea test kit after reaching my color change I am reading about .55 ml left. BUT from the instructions it says “amount used” so that leads me to believe that the amount to correlate on the chart would be .45 which is 6.4 dkh. Now if I took the .55 ml reading I think that would put me around 7.8 dkh which would be very close to the salifert test. Watching the RedSea video makes me believe that it is amount used so the 6.4dkh would be correct.

I did both test 2 times now 24 hrs apart for a total of 4 test from each kit all with the same results.

WTH? The instructions could be a little more clear on both. I must be doing one of the test wrong? I have read numerous reports that both of these are pretty accurate. My sailfert kit is not expired.

Lostinthedark
08/27/2012, 08:09 AM
I have the same kit. It's the amount used. So if the plunger line is at "0.70" you used .70ml and yoUr all is 9.8. I had Salifert and got inconsistent results. On their ph test it always reads just under 8 no matter when I tested. Brought water to the Lfs and ph was 8.4. I knew it couldn't have been right.

Lostinthedark
08/27/2012, 08:15 AM
Hey sorry. Messed that up. If plunger is at 0.30 then you used .70ml and kh is 9.8

advancebc29
08/27/2012, 08:23 AM
Hey sorry. Messed that up. If plunger is at 0.30 then you used .70ml and kh is 9.8

I take it you are speaking to the RedSea kit only? If so that is what I thought and what I feared.

I understand that the test will not yield exact results but 1.3 dkh is a huge difference. I am running a somewhat ULNS heavy SPS tank so keeping my alk in check and not on the high side is critical .

If I am sitting at 7.7 that is great and that is where I want to be. But if I am sitting at 7.7 and take the RedSea 6.4 and try to bring it up to 7.5 - 8.0 I will most likely cause a big issue with my tank as the last time I had a large swing in the plus direction I lost over 50% of my SPS.

Issue is that that my tank is dosed but I have not measured my alk or adjusted my dosing in about 4 - 6 months. (Yes I know BAD REEFER! but life and a new baby got in the way). My sps is now 4-5x bigger then before so I know they must be using more alk at this point.

ReachTheSky
08/27/2012, 08:35 AM
You measure it by the amount of titrant that was used, as Lostinthedark said. I would redo that test just to be sure.

That said, I use the Red Sea Pro kits. I've compared it to the Salifert kit which my friend uses and found them to be within +/- 0.2 dKH of one another.

advancebc29
08/27/2012, 08:51 AM
You measure it by the amount of titrant that was used


For both the RedSea and the salifert test?

ReachTheSky
08/27/2012, 09:02 AM
Salifert was nice and did the math for you in this case. You measure what's left in the syringe directly to the chart.

advancebc29
08/27/2012, 10:28 AM
thanks everyone. so it looks like I am correct in the way I read both the salifert and the RedSea. Now I just need to figure out why there is a 1.3dkh difference. Which I consider way too big of a difference between these test kits. Now I need to figure out what my real dkh is

Mavrk
08/27/2012, 12:54 PM
The Salifert kit could be old by now and giving inconsistent results. Either that or you are using the incorrect endpoint. As soon as the color changes that is the endpoint. Not when it reaches a certain color (this is true of all test kits unless noted otherwise as far as I know).

fishchef
08/27/2012, 03:34 PM
Honestly, I've been using various Salifert kits since '94 and I switched to an API dKH a couple of years ago and it works great. Can't beat the price and its fairly accurate as is the CA. The rest of my tests are either Salifert, Tetra, or Hanna.

bertoni
08/27/2012, 08:54 PM
How old is the Salifert kit? All kits tend to start reading a bit high after time, as the water evaporates from the titration solution.

sh8g8delik
08/28/2012, 11:50 AM
The Salifert kit could be old by now and giving inconsistent results. Either that or you are using the incorrect endpoint. As soon as the color changes that is the endpoint. Not when it reaches a certain color (this is true of all test kits unless noted otherwise as far as I know).

So it's when it changes color intially? or completely changes color? When i do my test theres always a little color left on the bottom that never completely changes its color until i add more of the solution. Sorry i am fairly new to this so just want to make sure i am getting this right. And sorry OP for hijacking your thread. I am using salifert as well.

hobbby3
08/28/2012, 05:52 PM
With the redsea kit you need to be sure you have the tip on when you suck up the titrant. If you put the tip on after you have a pocket of air that would count as titrant used throwing off the reading.

bertoni
08/28/2012, 09:47 PM
The Salifert kit should change colors and stay changed for 10-15 seconds or so, as I recall. That should be fine.