I'm getting some really confusing readings from my PH meter. It's just a Dick Smith brand. I was testing my 400 liter tank(after calibrating the meter with the PH 7 buffer) and the PH was at 6.4 so I put about a teaspoon of baking soda in a glass of water and thought I'd test the PH in the glass. Came up as only 7.6, weird should be a lot higher. Then I poured the water in the tank and thought I'd test the tetra tank. I rinsed the glass out and scooped a glass of water out to test. It came up as 8.2, I thought that couldn't be right so I put the tester into the bottle of buffer. That came up as 7 so I rinsed the tester and tried the glass of water again and it came up as 6.8. Odd that it should change like that.

I can't think of anything I'm doing wrong. I rinse it with clean water after using the buffer solution and before putting it away, I calibrate it each time I use it. I keep stirring until the reading stabilizes, but I'm still constantly getting confusing readings. I'm not particularly happy with this thing. I can live with it being so sensitive that if I put it directly into the tank just the heater being on causes it to bounce around by .5 each way...But half the time I put the cap back over the sensor it turns the meter back on!

Anyway, can anyone think of anything I might be doing wrong or have any advice?

I hate pH meters with a vengeance :evil: I have the problem of waiting for what seems half an hour for the stupid thing to stabilize so I can get a reading. It sounds like you are doing everything right. the only thing that i can think of is that the glass still had some residual bakeing soda in it after you rinsed it out giving rise to the high reading. The issue with the reading bouncing around due to the heater is novel to say the least, Has anyone else heard of electrical interferences (I take that’s what you meant?)Affecting pH readings??

If you had rinsed the glass out several times (which I am sure you did) then I would suggest borrowing / buying another pH meter and see if you have the same problems. For a ball park range the colorimetric test kits are pretty effective, and while the readings can be a bit ambiguous at times the are consistently ambiguous

I hope some one has a few more ideas on the issue.

Good luck.

Yeah, I meant electrical interference was effecting it. It's really not surprising actually. The sensor uses a small glass electrode filled with a solution of a known PH. When that is put into whatever you want to test it causes a very tiny current flow through the electrode into(Or out of) the known solution which the tester then amplifies. Obviously the end result is it's very sensitive to electrical interference. In addition to the heater it also gets quite a big twitch in the PH reading when turning the tank's lighting on and off.

The reason I got the digital meter is because I'm absolutely useless at comparing the colors. The meter is supposed to be accurate to within .01 PH, my eye-o-meter is accurate to maybe .5 PH.

Maybe when you want to test the pH, you take a sample in a clean glass and measure that. Then there will be no interferance!!??

If you reread what I posted you'll see that's what I've been doing. That or unplugging the tank for a minute.

The way you worded it sounded like you only did it only once. I was only stating the obvious because its amazing how many people look the obvious in the face and completely miss the point!

I NEVER miss the obvious. Nah, no way I'd ever do that. I'm far too smart to do that!

*Walks away and runs into a closed door*

Hehehe.

:-? hands Ira a cool cloth to stop him bleeding on the floor.

seriously though - I find the ph by using the 5ml of tank water and 2 drops of tester to colour it. My hubby being colour blind is my second opinion if I am not sure which colour has shown up. His colour blindness gives him an advantage with the blues/greens.

Had you thought of asking Brooklands or Southpetware or Masterpet re the digital differences???

The other reason it might give different results is because it is cheap! I have one too, and its never given a decent measurement in my tanks or in a sample taken from a tank. It maybe due to the low level of TDS is the tank water. Because I use RO and add only the minimum amount of buffering salts + CO2 and H2SO4 to balance the pH, there may not be enough electrolytes in the water for the pH probe to work well. It certainly works ok on a more concentrated sample (>200ppm TDS). My water is approx 20ppm KH. It appears the probe only works with a KH greater than 80. This is only in my tanks and there are probably a lot of other factors that effect it. It is interesting to note however, the Dupla Alpha CO2 controller states very strongly that the KH must be over 68ppm to work properly. It is for 1 of 2 possible reasons:

1: So the pH probe works

2: So you buy their very expensive KH buffer.

Back to the cheap probe. The Dick Smith item is very cheap for a pH probe. I got mine for approx $80.00 some time ago. A good quality probe usually costs wholesale about $250.00, - and thats just the glass bit. The meter part costs even more. These types of proffesional / industrial probes work much better. I tried one on my tank sample and it worked reasonably consistantantly. Had to give it back though, - cost too much to keep.

Unfortunately I can't even come close to being able to afford $250+ for a PH meter. I still feel guilty about spending the $120 on the dick smith meter.

*Mutter*Maybe someday if I get a real job...Shoulda stayed in the US doing desktop support...That was a great job...*Mutter*

Ira said...

> ... Shoulda stayed in the US doing desktop support...That was a

> great job...

I'm sure someone would hire you as a table leg here, can't imagine

it paying very well though... ;-)

Andrew.

Already done that job...And no, it didn't pay very well.

Hi Ira

Bought one from Dick Smith. Around $100. Could not get a steady reading. Went back to Dick Smith and the fellow there could also not get a steady reading. After about 20 minutes trying, he opened another box.

Same thing. So I bought the waterproof, automatic calibrating one for $190, he gave it to me for $170. And I never look back. The cheap one has a resolution of 0.01!!, which is ridiculous for a cheap model. Mine has a resolution of 0.1, which is damn good enough for me.

The electrode is easy to replace, whereas the cheap model is not.

John

I don't have a problem with getting a steady reading as long as there's no kind of electrical interference. Sometimes it does take a while to get to the right PH, though, seems like I keep stirring and the PH keeps creeping downwards for ages. Normally it's pretty quick though. I think the waterproof meter was over $200 when I was looking.

Hi Ira

It is also possible the electrode is old. Used up in a word

John

It's only about 3-4 months old.

Hi Ira

Take a quantity of water, test it, then go to a mate or a shop (with the testwater) , which sells pH meters and do a comparison. Then you find out immediately.

John

OUCH. I thought I'd stop adding baking soda to keep the PH up for a little while to see if it would settle somewhere not too low(Ok, and I got a bit lazy too). So, I tested today after 3 weeks and it was at 5.7. The fish seem ok, but I think that's definitely a too low.

Hi Ira

Are you fair dinkum with pH of 5.7? What sort of fish do you have which tolerate that kind of pH? My pH goes down to 6.5 in my mollie tank and I'm worried. Because pH of 5.7 is about the pH I have in my car battery.

Check your meter. It might need a certain service overhaul, called rubbishbin. Or if you use the conventional method it might need replenishing.

Aaaaaaaaaagggggggggghhhhhhhhhhh.......5.7

John

LOL John I quite agree. Passes rubbish tin to Ira

Yes, I'm absolutely sure of the 5.7. They're mostly south american cichlids, by the way. And there is no way I'm throwing away most of a weeks pay just because the meter gives me an occasional odd reading.

Hi Ira

I an not having a go at you. A small amount of humour injected should do no real harm. I really don't know what sort of cichlids you have. "South American" does not mean much. Most of them I saw in the Baench Atlas are in the region of 6 - 7.5. Then again, even that is meaningless unless one knows the exact species. So don't throw away you pH meter yet.

Having a 'normal' tank with an 'normal pH reading of 7 can go down to 6.5 or even a bit less. With little effect on most fishes. But 5.7 is a dangerous level IF you cannot control it.

John

5.7 is definitely NOT what I want it to be. I just can't find a source for anything to keep the PH up other than throwing baking soda in the tank every couple days. Maybe I should take Pegasus up on his offer to send me oyster shells, because I can't find anything like that locally. Maybe I should take a drive out to Porirua, I think a landscaping place there had crushed seashells a year or so ago, nowhere local does.

The fish are, more specifically, 2 gold severums, 1 green severum, 2 Geophagus Jurupari, 2 geophagus surinamensis, 1 pictus, 1 redspot pleco, 1 striped mystus, 1 silver(Now dark green) mystus, 2 bristlenoses, 1 firemouth and 2 blue rams. I think that's all of them.

Hi Ira

My water here in Melbourne has a dKH of 3 and a dGK of 4. Because all my fish died, I wanted to start again with african cichlids. the LFS sold me a powder which supposed to increase the hardness. IT DID. It's 20dGH and 16 dKH. A beaut. It is called african cichlid hardness salt. He also has the same kind of salt to increase the pH.

John

Yeah, there is proper PH type stuff. But it would be essentially doing what I'm doing with the baking soda except would cost me if I remember right about $30 for a 1 month supply.