new Salifert Alk test kit

[gflat65]

I just got one of the 'updated' alk kits from Salifert at the Chattanooga swap and have a question on the instructions I was hoping someone could help me out with. The instructions on this one don't mention subtracting the reading where the plunger is from 1, to show how much you used to determine the alk level in the tank. It says to turn the syringe over so the tip faces upwards and read the value from the chart. This can't be right, can it? I've never seen one where you use the position of the remaining solution instead of the amount of solution you actually used. There is air in the syringe, so if I gauge off of what is left in the syringe, the amount of air this time might be different than the next time, varying my results. I have .45 remaining, menaing I used .55mL. I'm pretty well dead on if I use the amount remaining to determine the value (.45mL=~8.8). I don't think that is correct, though. I think it should be the amount used to determine the correct alk... Can someone verify this for me?

 

[DMBillies]

Gary- I don't know how they changed them, but the old ones (bought about 8 months ago... I think I heard they were updated more recently than that) you just read the amount where the plunger was after doing the titration. I think the table does the subtracting for you (if you start at 1.0 and end at 0.2, you would look up 0.2 on the table, not 0.8). I think they just do that to make it easier to figure out and keep people from messing up the subtraction.

It makes perfect sense if you figure that the solution left is inversely proportionate to the solution used (as long as you always start at the same value of 1.0).

 

[crumbletop]

I think the same way, Gary, but that is the way my salifert alk test works. It is opposite of the way I think (and the way most chemistry stuff is done). So yes, mine has me invert the syringe and read the amount left rather than the amount dispensed.

 

[ocd_mariner]

Isnt this the way the old alk test kits were as well? You measure how much is left. The syringe is measured to 1 ml *without* the elongated tip you put on it when you draw in the liquid, so that accounts for the air in the syringe *with* the tip. You've still got 1ml of liquid in there. I haven't seen a new kit, so I'm just referring to the old one, pardon if its not the same.

 

[gflat65]

Sounds like it might be the norm, then. I've been using LaMotte. I had to switch back to Salifert because the Ca kits are so hard for me to be accurate on (they change to purple, then to clear blue, but bacjk to purple-disregard any color change back to purple after five seconds... I can get within a 20 mL range most of the time, but when you count to five and get to four and it changes back to purple on you, did I vary my counting speed, etc.-too much potential for variation on my part). I don;t have a problem with LaMotte Alk test kits, but since I made the switch, I figured I'd make it across the board. I may use the Salifert to guide me in finding the right ending point on the LaMotte, though, so it isn't wasted. All other titration tests I do (tank and work) you use the amount used, not the amount left over.

Thanks for the replies. Looks like I'm dead on in that tank, then. I'll start testing the rest (can't wait to have a more combined system...).