None. pH kits are all incredibly inaccurate until you're into the Really, Really Expensive range. Even then, proper training for use is required.

I cringe when people report their hand-held pH meter's results and happily claim that it matched well with their RapidTest kit's pH reading. Of course it did; both are wrong and tending toward 6.5-6.8.

Do I have a simple hand-held? Yep. Do I use it? Only as a relative reference for soils where I already know the pH...and I still don't trust it.

Could this be a good PH testing device?

Kelwayî Soil pH Meter (please see it on Amazon).

This post was edited by micnn on Mon, Oct 6, 14 at 2:27

I can't tell. A quick review says it's an acidity meter (readings over 7.0 are, at best, going to be inaccurate).

Off the cuff? I'd say it's as accurate as any other--or not very. It's certainly not a replacement for a soil test from a reputable lab.

Contrary to popular opinion, pH isn't a cause, it's a symptom. Even if your pH came back 4.5 (hey, mine did nine years ago!), what do you do about it? Lime? OK...what kind? Are you short on potassium, which isn't in lime but is an alkaline ion?

Similarly, a perfect pH of 6.5 can still be generated by a soil very short on calcium, magnesium, and phosphorus, but very long on (toxic) sodium. Your pH meter says you have perfect soil. Your actual soil says you have a ton of work to do.

In and of itself, knowing your pH isn't important. Knowing the ions and balances that comprise your soil's overall acidity or alkalinity is important.

Soils also balance differently. I set mine close to 6.2, but there have been cases where I'm reading a soil test and aiming for 6.8 because there's a trim margin of error.