pH Meter Question

I have the HANNA HI 98103. I found it for fairly cheap online and went for it. I calibrated it with 4.01 and 7 standard reference solution but even once I have it dialed in on the 4.01 when I rinse it and re-check it doesn't read 4.01. I'll re calibrate it and try again and it will show something new. It doesn't seem to measure consistently and the same sample of water can fluctuate by an entire point over 3 or 4 different tests. Also it claims it's fast but it seems to continue to change the longer I leave it in the water I'm testing.

I believe it could still be user error and not a piece of crap meter, but I'm not sure. So lets run through my technique.....

How long should I leave the meter in the sample? The calibration instructions say start with 4.01, leave the meter in for 1 minute then calibrate. Should I be leaving the meter in the water I'm testing for 1 minute too and go with what that says?

How deep should I stick the meter into the water sample? I use a shot glass worth of water to test, same with calibration fluid. If I just submerge the tip vs submerging it to the bottom of the shot glass I get different readings.

Should I swirl the meter? I've found a few places that suggest I should be swirling it in the sample while other places don't mention any swirling being necessary.

I'm going to pick up some test strips tomorrow and try a head to head test with the meter.

Any thoughts, comments, tips, or suggestions on this would be greatly appreciated! If I am an idiot that cannot use a pH meter, tell me! If my meter is shit, tell me! I can't spend $200 bucks on a nice pH meter right now, so if I must switch to just using paper testers, so be it. I just want consistent results for some peace of mind my pH is right.

Thanks!

First, forget the 4.01. Just calibrate to 7 and for that matter you can use distilled water to do it. A tenth doesn't matter a bit for that we are doing and if it is on at 7 it won't be off even a tenth at 5. The double calibration is for applications where closer tolerance is needed.

When you test water in a res turn off any agitation. Do it in the res and yes, swirl it around at first. It only needs to have the tip down in the water. Yes it will swing some but that should slow down. If it settles anywhere from 5.5 to 6.5 you are fine.

Thanks man. How long do you usually let it go before you call it? Or do you always wait for it to stop moving? I feel like sometimes it takes a couple minutes for it to stop

I never wait for it to stop moving. As soon as I know it's in the acceptable range I stop. But then I'm not as OCD about pH as some. Another thing, check at the same time every day, it varies by time of day.

Hey colorado lovin, hope I can deliver some insight into your ppm woes. I too, when I first started working with DWC, used that meter and in short; its a piece of junk . It was nearly impossible to calibrate when I worked with it, and when it finally was able to be calibrated, I found that it fluctuated heavily when it was testing a solution with a lot of nutrient particles. It seems that with meters like that, they simply are not suited for what growers need.

There are a few important factors though to remember about pH and what affects it. For one, any gas solutions that will evaporate over time will affect your pH, so if you are using tap water, it will be almost impossible to get an accurate reading that will hold over an extended period of time. Also, temperature change will affect the ion ration in your solution, thus changing your pH! (Chem 101 - your acid is H+ ions and base is OH- ions).

In my personal experience, I have found that the meter listed below have given good results and are not $200 and don't need to calibrated on a daily basis because they are quality parts . Also, when you calibrate, you want to fully submerge the probe on the machine, and swirling slowly is not a bad idea because it ensures uniformity in the solution you are testing.

http://www.hydrogardencenter.com/grochekphep4wpmeter.aspx

However, there are much cheaper alternatives which will provide a range to work with, but not precise in any way.

http://www.hydrogardencenter.com/phcontrolkit.aspx

If you have any more questions don't hesitate to ask!

Thanks guys, I appreciate the responses. I kind of figured my meter wasn't very hi-tech cause it wasn't very spendy. I've done some Google'ing on it as well and it sounds like it's primary shortcoming is what sexyroots just touched on... temperature. Evidently nicer meters can handle different temps, my meter can't. I didn't do so hot in chem in high school so it's no surprise I didn't think of temperature as a factor in pH balancing.

I appreciate the links sexyroots, those are actually the pH up and down that I have! I just need to get that test solution. That meter looks pretty nice too. $109 doesn't seem to bad either. Maybe for my next grow I'll pick one up. I still need a ppm meter so I think I'm gonna splurge for that and just finish off this grow with the low-tech strips/solution for the pH.

Once again, thanks to the both of you for your replies! +rep to both of you for the help!

Should get the PPM/pH Hanna combo meter for a few $ more. Kill two birds with one stone.

Ha I was wondering when you'd weigh in grow-twin.

Good call on the combo meter. I'll do some Google'ing