I use a TDS meter I got at Petwarehouse.com made by sharp.
NOT PETSwarehouse. Also I believe 3 guys aquatics has one made by Hanna which is less expensive and also a good product. They are located at http://www.threeguysaquatics.com/ As for the pH meter. I don't use one. Whatever works for you. I've learned via this list the key seems to be water changes. And low DOCs. -Dissolved Organic Compounds- I've had 8 spawns in the last 4 months and I'm a new guy. Less than a year breeding. This pertains to my South American fish not my Neolamprologus types. Hope this helps.
Jerry Jerry B's ApistoWorld