Great write up! Anytime I'm buying test (mostly salifert and last two for PO4 and Potassium I got from Elos) same question coming to my head... Is this test accurate? Especially potassium, I have heart buying Potassium test is just wasting money cause the only way to check it is laboratory. Will be great to check the accuracy of all popular test, the easiest way to do this is send water let say here: http://www.aqua-medic.com/aquariumwatertesting/ Then check same water home with all available tests and compare result. How many tests you have available? I understand is expensive but maybe with some members help it can happen so we all gonna know what to buy. That's only my two cents but I'm open to help.