conductivity is usually translated into TDS, total dissolved solids which can be loosely converted into gH based on assumptions about what the solids are. You can estimate kH this way also, but I think you need at least one other test added to this one to get any real accuracy.
When you say "one other test" do you mean like a liquid test. Basically what I am trying to do is have Discus fish. I want to have probes monitor the majority (if not all) of what I need to monitor. I currently have a CO2 system linked to a PH probe so it's relatively pain free knowing the PH and amount of CO2 in there. (I also have a drop checker for co2)
I read this on the conductivity meters website "This precision instrument is perfect for serious discus keepers who add trace elements to pure water to achieve a reading of about 70 ÁS. Also useful for determining membrane effectiveness of reverse osmosis units. Regular tap water measures about 300-500 ÁS; good quality RO water measures 5-15 ÁS."
I'm guessing this is for measuring AFTER I use pure RO water and add something like discus buffer...
Anyhoo, I guess what I'm trying to do is have my ph probe, my drop checker, and my __________ (fill in the blank here) so that I can open my aquarium stand, glance down and see that my water looks good for my discus. Is this possible with probes alone (if so, what probe will be best for hardness if not this one?) or will I need to resort to my trusty API liquid test kit?
Conductivity is great for adding a mineral blend to RO water. My tap is about 50 TDS, so I add cichlid salts to 150 ppm for Lake Victoria, 300 for Tanginika. that sort of thing. It doesn't tell you what you have in the water, but if you start with RO (0) and add, you know very well what you have. It also shows when you need to change the cartridge in the RO. The thing it doesn't do is the only kH for the pH/kH chart to tell you the CO2 level. But if the drop checker gives you that, I think you may be good to go. If your conductivity in the tank is creeping up, change water it is likely nitrates.