Constant pH meter?

What are some decent pH meters I can just mount somewhere and leave in my res, obviously will have to clean/calibrate every so often.

Was looking at one of the Hanna ones but people say they are having alot of interference problems with them and the ballast.

Any help?

Budget is like ~200, although ~150 is ideal.

Thanks.

I like the Hanna ones and I've never had any problems with them. I have Lumatek Ballasts and I've never experienced any interferance. I know that Blue Lab also makes good meters but I am not sure if they are meant to stay in the reservoir. The Hanna Nutradrip Continous Meter is designed exactly for that.

Buy a BlueLab meter and never look back again....