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 creamcorn
mad scientist
 
Registered: 03/13/06
Posts: 2,962
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 Rapitest pH meter? 
#5891358 - 07/23/06 04:31 PM (17 years, 8 months ago) |
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anybody have one of these or something like it? saw it for $13 bucks today so i thought what the hell and grabbed it. its for "soil" only, can't measure pH of liquids, but seemed like it could come in handy for casing/subs.
tried it on some coir just now. read about 6.5 straight up, added some coffee grounds, mixed well and let it sit, read closer to 6. added some gypsum and a tiny bit of hydrated lime, mixed well, let sit, measured again, and was back up to 7. seeems like it works. i just have a hard time trusting any sort of "instrumentation" that's so inexpensive.  so was just wondering if anybody has one of these and if it seems to be reliable to them...
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Anonymous
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Post deleted by Anno [Re: creamcorn]
#5891363 - 07/23/06 04:33 PM (17 years, 8 months ago) |
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fastfred
Old Hand
Registered: 05/17/04
Posts: 6,899
Loc: Dark side of the moon
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Re: Rapitest pH meter? [Re: ]
#5891507 - 07/23/06 05:15 PM (17 years, 8 months ago) |
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They don't work. Even for soil you'd be better off just guessing. The electrodes corrode and the moisture level of the soil has more effect than the pH. I got a .99 one once on sale even though I knew they didn't really work.
I asked the store owner how well they worked and he said "Well it's on sale for .99, it works as well as any pH meter you'll get for a dollar," so I figured what the hell. After using the unit I figure it wasn't even worth the .99.
-FF
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liamtheloser
Advanced Idiot
Registered: 06/07/06
Posts: 1,453
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Re: Rapitest pH meter? [Re: fastfred]
#5891838 - 07/23/06 06:42 PM (17 years, 8 months ago) |
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I use litmus paper or aquarium drops... they both work really well.
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 Eraserhead
Lost Soul
Registered: 05/26/06
Posts: 1,363
Loc: Earth
Last seen: 14 years, 5 months
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I make a slurry with distilled water, and a hanna phep4 water pen. My soil comes out to 8.1 when loaded with oysterflower, I assume it's fairly accurate this way.
Everythign I've read on other cultivation forums say those soil probes are bunk.
The good soil probes are in the $100+ range
I was actually interested in purchasing this one at one point in time
it's around $100
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jcee
Stranger
Registered: 06/06/06
Posts: 234
Loc: dallas tx
Last seen: 14 years, 2 months
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Re: Rapitest pH meter? [Re: Eraserhead]
#5892641 - 07/23/06 10:16 PM (17 years, 8 months ago) |
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ya i have that same one got it lowes
I have used it for my substrates and casing and it been working like a charm for me
if you clean it most likely wont corrode for a while
Edited by jcee (07/23/06 10:20 PM)
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Tippinthru
contented
Registered: 04/07/05
Posts: 1,131
Loc: "The Garden"...
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Re: Rapitest pH meter? [Re: creamcorn]
#5892657 - 07/23/06 10:27 PM (17 years, 8 months ago) |
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HB-2 Kelway is the one you want.
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Perfection is attained by slow degrees; it requires the hand of time...
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udontknowme
Psychonaut
Registered: 04/20/06
Posts: 198
Loc: The Funk Parade
Last seen: 13 years, 9 months
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Re: Rapitest pH meter? [Re: Tippinthru]
#5892677 - 07/23/06 10:37 PM (17 years, 8 months ago) |
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I have the same one for $13. Seems like it only works well if you keep the tip REALLY clean. use the little white cleaning pad it comes with before each probe.
Sometimes if it doesn't read, I'll take a fistfull of material and sqeeze it and then probe it. still dont't know how accurate, but it gives you an idea. Try it on different things to get an idea.
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creamcorn
mad scientist
Registered: 03/13/06
Posts: 2,962
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yeah it obviously read, and moved back and forth with the probes as i'd expect as i made changes to the substrate.
so i dunno i wouldn't trust it as being accurate for "absolute" measurements, but for "relative" measurements just to observe how things might swing. i guess we'll see how long it lasts, according to all the cleaning instructions and like you mentioned it even comes with a cleaning pad... i dont doubt its gonna be a corroded mess.
its too bad because it is a lot easier than the test strips. ill invest in a "real" one soon enough... 
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fastfred
Old Hand
Registered: 05/17/04
Posts: 6,899
Loc: Dark side of the moon
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Re: Rapitest pH meter? [Re: creamcorn]
#5892975 - 07/24/06 12:23 AM (17 years, 8 months ago) |
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Here's why I say they're bunk. If you test the same thing several time's you'll get several different results. It seems to depend entirely on the exact contact it's getting with the soil. So if you insert it 5 times you get 5 readings. If you just shove it a tiny bit further into the soil it will read different.
Even the expensive pH probes are a PITA. You have to store the electrodes in electrode storage solution and frequently calibrate them with buffered solutions. pH strips are way better and easier. I have one and never use it, by the time I'd be able to get it setup and calibrated I could have already done a dozen strip tests.
-FF
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Tippinthru
contented
Registered: 04/07/05
Posts: 1,131
Loc: "The Garden"...
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Re: Rapitest pH meter? [Re: fastfred]
#5893730 - 07/24/06 07:27 AM (17 years, 8 months ago) |
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Again, Kelway HB-2 is the one you want.
It does pH, and/or moisture/saturation level.
It is on the money ACCURATE, every time.
P. Stamets uses one.
They are NOT cheap.
http://www.shroomery.org/forums/files/06-01/619752532-ph_perfect.jpg
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Perfection is attained by slow degrees; it requires the hand of time...
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