In article , says...
Hello,

I was wondering if you guys could recommend a probe or meter which tests the
water for the following:

- Nitrite
- Nitrate
- Ammonia
- PH


I don't think that you will find an all-electronic solution for your tests except
pH. Even for pH, there are limitations to the pH probes that do the actual
sensing.

The biggest limitation of the cheap test kits that are sold for the aquarium is
that the comparison is a printed card (reflected light) while your sample is a
clear tube (transmitted light). I prefer a swimming pool test kit for pH, which
does provide a decent reference printed.

Nitrite and ammonia are easier since you are usually verifying a reading of 0 and
not trying for an accurate measurement. I don't like any of the nitrate test kits
because they all seem to produce only shades of the same hue, which is really hard
to read against a printed card.

The best bet is a colorimeter that reads the vials for you. You still have to
sample water in test tubes and dispense reagents to cause a color change. But the
reading process is much less error prone than comparison with the printed card.
Lamotte makes one that is very expensive ($650) but claims to read 43 parameters.
For about $230 you can get the Medusa CHEMITESTER 750. This one supports tests for
ammonia, nitrite, nitrate, pH, phosphate, and copper. It is available at
CustomAquatic.com. I don't have any personal experience with it.