[repeated from earlier in the thread and edited for clarity] [RE frequency of tests] "WHen cycling, test once a week until the second week, then daily. If you think you really are cycled, and might have missed the spike, try one snail, one crab. If they stretch out and do fine and look happy, you're probably fine. If not, get them out until another few days.
During qt: Test qt water daily, and test morning and evening if you have a small qt. Watch your water level: SALT DOESN"T EVAPORATE. If you don't top off with fresh water, you end up with the Dead Sea, salty as all get out.
Test dt parameters before doing any change or dosing, so you have a benchmark. And write it down in a logbook so you can look it up if something goes wrong.
Also test again the day after (or 8 hours after if in a rush) you've done a change, because it takes time for stuff to dissolve and work its way along. Just give it time.
Test alkalinity weekly until you're sure you can look at your corals and pretty well see how the chemistry is. This comes with experience. But experience can lead you down a primrose path of 'all's well' until it isn't. If you have stony coral and are using kalk, just testing the alkalinity will tell you how it's holding, but testing mg occasionally instead will tell you how close the tank is to needing more mg. With a large reservoir and kalk, you can keep it all in balance for a month without needing to do more than add fresh water...and that's with kalk and stony coral: ask me when you get to needing it.
If you're fish-only, test salinity, nitrate, alkalinity weekly. FIsh don't tell you they're suffering from the water quality: they just keel over.
And test any time you think something's off.
The tests do expire with time, so no sense hoarding them forever. Use them. NOTE your expiration date, and don't use them past that. And keep a notebook of your readings: always dose to prevent a tank from exiting the 'safe' zone, eg, 8.2 alkalinity is the reading: I'd dose and check my magnesium, because mg is the lock that secures the door. If alk is falling, probably mg has dropped. Think of it as a tripod, but mg is the one that's going to go down first. Fix it first, then fix the alk and cal in that order. There's a file inside the SETTING UP file called DIRT SIMPLE CHEMISTRY that explains how all that works. It's just that one is reliant on the other, and the weekly tests let you understand how fast your chemistry slips in that unique tank. Dose before you get to a bad zone.
And test again before you dose again. Always give it time to dissolve.
There's also a way to 'cheat' on the drop by drop Salifert tests if you've got that logbook up to date, and unless the instructions (read them!) give you a time delay or duration over which something must be done: rush through your drops until you're 'near' the last reading. You'll also see a 'flash' of the 'change color' before you really get there, which is another warning you're approaching the color change point. For our purposes, that's a good time saver, and you still get a good result."