Alkalinity test - 1st timer - help!

[miserkris]

Just tested my Alk with elos kit. Took 13 drops to turn from light cyan to light yellow. Turned yellow on 13th drop. So does it have to turn to real /dark yellow? Mines was just light yellow.

The instr say that Dkh is # of drops/2. So mine is ~ 6.5. Ideally should be bet 8- 12 dKh right?

Did I measure mine right? Does it mean my alk is ~ 13/2 = 6.5?
thx!

 

[HighlandReefer]

Elos test kits are designed for fresh water, they read 10% low. This means you need to subtract about 10% to get the proper alk reading when using salt water. So your alk is actually around 6.8 X .90 = 5.85 dKH.

The recommended alk level is between 7 - 11 dKH. Raising it to 8 is reasonable to provide some error and drop in alk from coral consumption.

To raise your actual salt water alk level to 8 dkH you will need to raise your level up to 8.8 using the Elos kit. I would use the Reef Calculator and baking soda to do this.

Reef chemicals calculator
http://home.comcast.net/~jdieck1/chem_calc3.html

 

[HighlandReefer]

Sorry, I am getting tired. :lol:

I edited my last post.

 

[bertoni]

I think 8 dKH is a fine level to target. I have heard varying reports on how the Elos is calibrated, but I thought the manufacturer said it was for saltwater use. I'll have to check, but alkalinity kits seem to be a common source of trouble, anyway.

 

[cshutchinson]

They seem to say both....

"Precise Titration kH (Carbonate Hardness) kit for Freshwater/Marine Aquariums.
7°-12°dKH (Marine)
3°-7°dKH (Freshwater)
Batch validated using NIST samples and independent seawater lab.
Precise calibrated dropper.
"Safe Reagents". Reagents and testing procedures are based on Low Risk Reagents.
50+ tests per kit, depending on KH levels."

Now I am confused.

 

[bertoni]

Well, that writeup is not very helpful. I'll try looking on their web site. It might be calibrated halfway between marine and freshwater.

 

[HighlandReefer]

They seem to say both....

"Precise Titration kH (Carbonate Hardness) kit for Freshwater/Marine Aquariums.
7°-12°dKH (Marine)
3°-7°dKH (Freshwater)
Batch validated using NIST samples and independent seawater lab.
Precise calibrated dropper.
"Safe Reagents". Reagents and testing procedures are based on Low Risk Reagents.
50+ tests per kit, depending on KH levels."

Now I am confused.

The kit can't be accurate for both fresh and salt water. You need to titrate down to a pH of 4.5 for freshwater and down to a pH of 4.2 for saltwater. That leads to a 10% inaccuracy one way or the other.

 

[HighlandReefer]

FWIW hobbyists can use the acid titration test and a properly calibrated pH meter to detemine their alk level much cheaper. It is not difficult to do and equipment from an old test kit can be used. The acid titration uses a larger volume of water which is more accurate. The acid titration uses a pH meter to determine the proper end point which is much more accurate then the dyes used in test kits (similar to test strips) & you know exactly which pH you are titrating down to. There are too many problems with hobby grade alk test kits IMHO.

 

[HighlandReefer]

Randy provides additional details regarding the above discussions in this article:

Chemistry and the Aquarium: What is Alkalinity?
http://www.advancedaquarist.com/2002/2/chemistry