I've been trying out a few different KH test kits and figured I would post some of my experiences with them. Unfortunately, because I don't have access to a significant amount of KH standard, I can't really comment on the accuracy of the tests... I will however, show photos of the test kit components and talk about the actual testing process as well as the clarity of the color change. (I'm typing up an overview of the instruction for each kit to illustrate testing complexity for actual instructions, please see packaging...) Here are the three KH test kits that I have. They are all pretty new kits, each purchased within the last two months, Salifert, Elos and API: Salifert: ~$16 (100-200 tests depending on resolution) Instructions: 1) Add 5ml of tank water to test tube using syringe 2) Add two drops of KH indicator to tube and swirl (I find the indicator bottle a pain. It's quite messy and stains everything.) 3) Fill 1ml syringe with nozzle adapter attached with KH solution up to 1ml line 4) Add drops of KH solution until test changes from blue/green to orange/red or pink 5) Check number of ml's of KH reagent left in syringe and read corresponding dKH value in chart. The nice thing about the Salifert kit is that it now includes a little dKH standard of 7.3dKH (+- .3 dKH). This test is a little more involved than the other two because you need to add the indicator drops, fill the 1ml syringe precisely and also look up the corresponding dKH value in the table. The other two tests as you'll see are much simpler to execute. On the plus side, the salifert kit is more precise than the other two, presenting values in .3 or .4 increments. Also, since the syringe is graduated, you can infer a dKH value that is between two ml readings by splitting the difference. Next up, Elos: ~$18 (approx 60 tests) Instructions: 1) Add 5ml of tank water to test tube using syringe 2) Drop KH reagent into the test tube one drop at a time, swirling after each drop. Count the drops and stop after you observe a color change from Cyan to Yellow. (I find this color change very subtle and hard to read.) 3) Multiply the number of drops by 0.5 to find the dKH Elos recently changed their KH test kit from a 1 dKH precision to a 0.5 dKH precision kit. I actually really dislike this change because I can barely tell when the color changes from Cyan o Yellow. I used to be able to tell the change much more distinctly. That said, the quality of the test tube and syringe are really nice and the test is quick to perform provided you can detect the color change. Finally, API: ~$8 (Between 100 and 130 tests I think, they don't provide a number in their packaging...) Instructions: 1) Fill test tube with 5ml of tank water by dipping and then spilling out water up to the line on the tube. They don't include a syringe. (This tube is pretty crappy... it's really tall and thin and I find it difficult to get the water level to where I want without a syringe. I actually just use the Elos 5ml syringe to fill the Elos test vial and use that to test instead of the API vial.) 2) Drop KH reagent into the test tube and shake between each drop. Count the drops and stop after you observe a color change from orange to green. This color change is extremely distinct, much more so than either Salifert or Elos. 3) The number of drops is equal to the dKH of your sample. -------------------- As I mentioned before, I can't comment on accuracy since I don't have enough dKH standard to compare with and I don't want to burn through the little 7.3 dKH included in the Salifert test kit. That said, I can rank the tests on the following criteria: Price (Cheapest to most expensive) 1) API 2) Salifert 3) Elos Salifert might actually be cheaper if you use their low resolution mode and their 200 test estimation is accurate. API is cheap from an initial cost perspective. I picked my kit up in SF for only $8.99. Cheap is nice in that it doesn't discourage me from testing as often as I feel like. Quality of components (hardware, not reagents, since I have no way of measuring reagent quality) 1) Elos 2) Salifert 3) API The Elos kit is really nice. The 5ml syringe has a rubber stopper and the test tube is glass. The Salifert kit is fine, but the components are cheaper, i.e.: no rubber gasket and plastic vial. That said, the Salifert components work just fine for their purpose... I hate the API test tube. It's so thin that you can't swirl it well. You're better off ditching that tube and using the hardware from either a Salifert or Elos kit. Precision 1) Salifert 2) Elos 3) API The Salifert kit is precise to 0.3 dKH, the Elos kit to 0.5 and the API to 1.0. The Salifert is probably even more precise since as I mentioned you can read between the MLs on the syringe. Ease of Use 1) API 2) Salifert 3) Elos Once you get over the 'filling the vial' crapiness of the API kit, it's dead easy to use. The color change is by far the most distinct and the drops method is very easy to execute. There's no looking up value on a separate piece of paper, etc. On top of that the KH dropper is easy to open and drops cleanly and easily. Next, I like Salifert. I know there are more steps and there's even a table you need to look up, but the big reason why I think Salifert is easier than the Elos is because you can actually see the color change. Maybe I have a bad test kit, but I really have a hard time discerning the change on the Elos. It's to the point where i actually doubt my reading and redo the test to confirm. ----------------- Overall, my daily test kit is an API. I know some people have questioned their accuracy, but what I did was just test the API kit against both the Salifert and Elos to ensure that it's at least inline with the other two. The Salifert I will use for times when I want a little more precision (i.e.: tuning a CA reactor) or when I have a little more time. I think this Elos KH kit will be the last one that I buy. I used to like them before they went down to .5 dkh, but now I can't recommend them because they're so hard to use.