PH Meters

[Savant]

I am talking about the types which you affix permanently on the tank to constantly measure PH. I note that some run on batteries and some run on electricity... Which type is better?

Which brand is recommended?

Do they need to be constantly calibrated?

[celticfish]

Battery operated one are called "pens".
These need to be calibrated about every three months.
But may be more often depending on your usage and how you store them.

Electrical one are called "meters".
These are calibrated about every month so you have certainty.
The probes also need to be change every few years depending on make.

For brands, I'm not the best to comment.
But I did recently buy a pen made by Dymax.
I was skeptical when auntie reccomended me.
But when I saw it, it was a good design.
I lost my last pen when I dopped it in the tank.
This one is water proofed and the electrode can be changed like the Dennerle one I always wanted.
But I heard thats about $300+!

[joeyttk]

how about aquatronic ? they measure more than just PH