I think that's key. I think what's more important is the ballpark figures and the week to week trending.

If you really want accurate alkalinity results then you can do what we do in the water treatment industry, use methyl purple indicator and N/50 sulfuric acid to titrate. The N/50 sulfuric acid is very dilute and harmless. Using a 50 ml sample of tank water, add 4-6 drops of methyl purple indicator and add N/50 acid until the color changes from green to purple. Every ml of acid added is 20 ppm of alkalinity, so 6.5 ml = 130 ppm alkalinity (dKH 7.3). A 4 litre container of N/50 sulfuric acid is about $82.00 from Fisher Scientific. That's good for over 600 tests!

I also use an industrial test method for calcium and magnesium. It's 100% accurate and much cheaper in the long run.

The commercial test kits are not very good and very over-priced. Like the commercial liquid calcium and magnesium additives, the mark-up is scandalous.

The one before my last Salifert test kit came with a Alk check solution. Maybe put up a post looking for some.

btw, both my kits check at 7.0dKH with it.

Hmmm
 

I have the API test kit for dKH and Ca and have found them consistently low lately...6-ish and 380-ish. However, when I dose up to a dKH of 9 and Ca of 420 according to the API test the colours are way better in the acropora so I suspect the tests may be correct....I am soooo confused-ish...:lol:

Ok so I tested again this morning....

API 8.5
Salifert 12.5

tested the check solution which is labeled 7.3....

and got 11.5 *wonders if salifert tests the check solution with their test kits*

so if I subtract 4 from my 12.5 reading I get 8.5 which is what the API test reads:neutral:


The second salifert test kit from the shop was off the charts...according to that one my dkh is over 16.


I hate test kits!:neutral:

Does a person have to use a 50ml sample of tank water? Could I use half that and then 2-3 drops of methyl purple and then for every 1/2ml of sulfuric acid the solution is 20ppm of alkalinity? I ask because $97.95 for the 4L acid and $13.85 for 120ml of the dye plus some tax and shipping for +600 tests isnt much of a deal. But getting twice that many would then make the idea start to make sense.

The cost looks like it would be about $130 for 600 tests which means I would get 4.6 tests for every $1 spent. A seachem alkalinity kit is about $18 for 75 tests which is equal to 4.1 tests per $1. Then again most of us only test once a week at most so 600 or so tests would last 12 years... I think this might require a group order.

https://ecat.fishersci.ca/(fw4tt355o...aspx?cid=20639
https://ecat.fishersci.ca/(fw4tt355o...px?cid=3640757

FWIW the only fresh alk kits I've ever had trouble with are Salifert. I've seen Nutrafin kits get wonky after 6 months or so but fresh ones are usually pretty good and the replacement solution is only $3. Never used Elos much, seems to me like it's the same indicator as the Nutrafin at a different concentration.

You'll never know what is up for sure unless you have a standard to check against. If you have a scale that measures grams you can do this:

1L RO/DI + 148g dry sodium carbonate should give you a 140ppm | 2.8 meq/L | 7.8dkh solution.

Get sodium carbonate (washing soda) by picking up some Aquarius pH+ pool stuff at Crappy Tire.