Jump to content

pH inconsistent readings

Recommended Posts


Hi all, 

Seems all I'm doing is posting problems on here at the moment. Ho hum, hopefully things will stabilise soon so I can get back to just enjoying my new tank. 

Anyhoo, had a bizarre situation come up over the weekend whereby my Dupla electrode starting showing a huge drop in pH but my pH pen and permanent colour tester in the tank are showing closer to expected values. 

Some background: 
- Tank [1220x930x800] filled with water and cycling (with daily top ups of Stresszyme) commenced mid-December (additional sump is 1800x400x400) 
- Tank has a lot of plants 
- Cherry Shrimp introduced a couple weeks later and doing quite well 
- High tap water pH reduced by automated CO2 injection plus IAL's in sump and tank 
- pH usually between 6.8-7.1 
- Water changes done via RO water into a water tank; shrimp gH/kH+ added to remineralise during water changes (along with Stresszyme) 
- No additional livestock put in until Australia Day last week. Livestock added: 7 discuss; 12 rainbows; 30 cardinals (had a few cardinal deaths since then and one rainbow was a little dodgy but is in quarantine now and doing much better; discus are doing great!) 
- On Saturday I added 4 blue rams and a big bolbitus 
- Other water parameters (that I measure): TDS: approx. 300-350; Ammonia: nil 

- <Update>: Got home and tested gH and kH: Results = gH 11 and kH 7
- Electrode is in the sump in the final partition where the main pump, chiller pump (inflow and outflow) and UV pump (inflow and outflow) all are as well. 
- Distance from main pump (sump) to tank is about 10 meters. Sump is set up in an external (plastic not metal) shed and doesn't get much direct sunlight. 
- CO2 goes directly into tank (not the sump) 


Yesterday I started getting very strange pH readings via the Dupla electrode. Since Thursday it's consistently been 6.9-7.05 but then dropped yesterday to 6.4. I recalibrated it and tested it a few times with calibration solution and it seems fine but the actual water readings seem out. I did a 25% water change and I know my water tank water has higher pH so the readings should've gone up. pH slowly went back up to 6.7 during the water change but then dropped to 6.1-6.2. 

I then got my pH pen, recalibrated it as well and it showed 7.5; it's usually 0.3-0.4 above the Dupla electrode. 

The permanent pH colour tester inside the tank was showing 7.2-7.4, much closer to the pen than the Dupla electrode. 

I thought maybe the heat of the day was affecting the electrode but the water temperature was consistently around 28-28.5. 

It's just very strange that I'm getting such different readings across the 3 devices, with the electrode showing a fast and significant fall. Given the pen and permanent colour tester are close to each other and show what I'd be more inclined to expect, they seem more correct. That suggests the electrode maybe out. But when I put the electrode into the 7 and 4 pH calibration fluids, it hits them right on. 

It's been suggested to me that all the pumps in that section of the sump maybe circulating the water too much for the electrode or that the magnetism of the main pump maybe influencing the electrode but if that's the case, it would've been happening before not just all of a sudden. 

I thought maybe the cooler water from the chiller may have been throwing off the readings but checking the reading all through the night until about 12am they remained around 6.1-6.2; although it was a hot night and the chiller kicked on and off throughout the night. 

<Update>: Electrode is definitely wonky. Got home today and it's reading pH 4.9-5.2, with heavy fluctuations each second of anywhere up to +/- 0.06. Moved it out of the sump and into a quarantine and same thing still and quarantine tank doesn't have circulating pumps or a chiller.

I'm now looking to order some pH reagents from Hanna Instruments so I can fire up my photometer to test the pH with that to get a very accurate reading. I've also closed off the CO2 until this is sorted. 

Has anyone had a situation like this? Any thoughts?

Edited by kapp
Test results for gH and kH and new electrode readings

Share this post

Link to post
Share on other sites

Hope you sort it out.

Can you just replace the electrode with a new unit?



Share this post

Link to post
Share on other sites

I have heard of similar problems before with these type (not that particular brand) that have issues when it comes to recalibration. The exact reason I am unsure but I tend to agree with JayC.

Or reading everything you are going through to apply an age old theory which is the KISS principle. At the end of the day sounds very painful especially if only keeping cherries. Also if I read correctly it is still only a couple of weeks old and IMO will definitely still be cycling which combined with Co2 (Not really a fan) both of these can cause fluctuations in ph levels and these can also change throughout the day. I liked to do my testing at similar times when eveer checking so that there was consistency. Like I said just my opinion.

What I will also say is the most important thing I learned over many years the hardway.... KISS 

Share this post

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Must Read SKF Articles

  • Register today, ask questions and share your shrimp and fish tank experiences with us!

    Join Our Community!

  • Posts

    • beanbag
      Another thing you can do to avoid rescaping: Just take some of the fresh soil and put it in your filter.
    • Zenplay,thailand
      Thx ^^
    • sdlTBfanUK
      Hopefully the fish has just damaged itself as you say, mine do that sometimes, although the changes in the water will undoubtedly have caused them stress and the water they prefer was the water you started off with? There are sections on this forum dedicated to fish, I used it when I decided to try a Betta and got great advice from JayC and this Betta is doing way better than any I have tried before because of all the different things I did/do this time! https://skfaquatics.com/forum/forums/forum/116-fish-keepers/ Great to hear that the shrimps are doing so well. I think it is natural for the berried shrimp to hide away when they are near to birth as it protects the newly hatched shrimps when they are born, and the babies don't move far when they newly hatched either. There would be little to gain at this stage in getting more shrimps before getting a bigger/new tank, it may even be detrimental? I admit to being lazy sometimes and not topping up the tank between weekly maintenance/water changes (disgraceful really as I keep a 1litre bottle of RO water right next to the tank anyway), in which case I end up taking out 2litres and putting back 3litres at the next change, but need to make an allowance for the fact the TDS will change. When I set up the new Taiwan bee tank I measured the water I put into the tank at the start (assuming the measuring jug is anywhere near accurate) so that is how I know there is 28litres in the 35litre tank - it is a good idea to do this WITH A NEW TANK (but with everything in the tank, heater, filter substrate etc) as it is so much easier to do at that point anyway. I did the same with the Betta tank and that has 20litres in a 25litre tank (the one you were thinking of getting at some point). Without the exact figure to put in the spreadsheet then it won't be 'accurate (can still be used to give you as near an idea as needed though)', especially on a small tank! It works to the digit with mine. Even if you empty the tank and refill it probably won't be that accurate as the soil will have absorbed some water, so best do it first fill of new tank. Your water parameters are looking good and pretty much there now so all else being well you should be able to go back to once a week maintenance/water change. I don't know much about Nitrite/Nitrate as I have never had any readings, apart from the old fish/cherry shrimp tank which has always been 50 nitrate for years, probably because there are too many fish but there has never been a problem in that tank? PURELY AS A GUESS I would think the duckweed may have caused the problem/imbalance, but that is ONLY a guess based on I used it once and swore never again, I use water lettuce now, though that isn't perfect either as the routes grow so quickly that I have to trim those every week, but still a lot easier than duckweed.  Simon
    • sdlTBfanUK
      Thanks JayC, I think it is called a Geode, that was what it was sold as when I bought it in US many years ago though it could be something else? I think it is some sort of meteorite? Hopefully, as you say, now it is removed the PH may start to drop and I have put one in some prepared water to test in a week. I will also just see what happens with prepared water left out for the same period just to see what happens with that. Simon
    • sdlTBfanUK
      Those are very good quality shrimps and photos. Simon