We have used the Hanna combo meter like that and works very well.

But you can get milwakie ph meter for about 20 bucks and a TDS meter for about the same. We use them more than anything and are happy with them . the combo is just a backup. An expensive one at that.AquariumPlants.com Largest online sales / service site for the live aquarium plants & aquarium products community.

Here is a good place to get a ph meter. if you look around you can find a tds for not too much also. This meter has been used by my bro for 2 years and me for over a year. You will need calibration solution also so check what kind you need. I think 7.01 is what it is.