does anyone recommend a good ec/ppm/ph meter that i can leave in the res?

as i am using an autopot system, i want to use something that is as easy and low maintenance as my autopot system.

also i want to know if i can transfer it into my other 2 resovoirs??

i have 3 x 200 litre tubs and i want something that can do all 3, i dont fancy spending huge amounts of money using 1 per tub haha.

what are the experts views on what to use to cover this???

rep added to good answers!!!!!!!!!!!!

does anybody have the blue lab guardian monitor? would this be good? http://www.getbluelab.com/shop/Bluelab+Guardian+Monitor.html