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Discussion Starter · #1 ·
I got a new pH/TDS pen today and I don't know if its working. I calibrated it with 7.0 pH buffering solution. When I try to measure the pH the display keeps going up. It won't stop moving. I'm testing 20 ml of sample water per the instruction manual. Is my small sample off-gassing CO2 so fast that it causes the readout to keep going up? 20 gallon aquarium. dKH is 5. The CO2 has been cranking at 4.6 bps for more than two hours. The drop checker is medium green late in the seven hour photoperiod. The lights are not very bright. Sorry no PAR. The pH pen indicates 7.07. So maybe it's working. That's consistent with the drop checker. Have the plant's grabbed that much CO2 during the course of the photoperiod?

The TDS of the aquarium water reads 590. The TDS of tap water is 390. The TDS of distilled water is 0-10. I have been doing weekly 50% water changes for eleven weeks and the discharged water has been dirty. The filter box is clean. Their is some Fluorite in the substrate. I have a big 13 year old piece of driftwood with some other smaller pieces of driftwood. The gravel is ornamental other than the Fluorite. There are no rocks. I have been following a low dose fertilizing regimen. Concentrations of fertilizers are under 50 ppm. There are no fish. dGH is 5. Is this normal? Or is 590 TDS too high?

I just turned the lights off. I'm letting the CO2 run into the night to retest the pH. I've never used a pH/TDS pen before. I thought it was going to be great but now I'm just confused. If 590 TDS is too high does that mean I'll have to reconstitute RO/DI water? The plants are doing well enough. Here is a water report link from 2018:


This old report shows an average TDS of 186. Could all the fires we've had recently in Southern California have raised our TDS since this report was made? Something is wrong here. The plants are growing though. Maybe they are ultimately the best arbiters of truth.
 

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I have a separate ph and tds meter. I found when I test distilled I get 5 to 10tds when My ro di i I get 0. My ph meter takes forever like 5 to 10 minute to stop moving. I found if I use a cup and leave it in there I get different readings then just the tank. I'm guess residual minerals or something affects the ph.
I would just test your ph before co2 and after. Also run a air stone that previous night to make sure the c02 is all off gassed for accurate measurement.
I bought a calibration solution for my tds meter. Not sure if it's needed tds is just relevant to show change really.
 

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Not to hijack, but I question the accuracy of mine too. Bought separate pH and TDS meters recently for about $32 total, so maybe I got what I paid for. But the pH meter doesn’t stop moving (in my case, lower over time), and though the TDS meter seems to show limited movement itself (like between 170-180 ppm) the temp thermometer it also happens to have is consistently reading 7-10 degrees cooler than the actual tank water temp (I have a temp controller and 2 quick-read thermometers and those three are always showing the same actual temp). So I don’t trust either meter.
 

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Discussion Starter · #4 ·
I have a separate ph and tds meter. I found when I test distilled I get 5 to 10tds when My ro di i I get 0. My ph meter takes forever like 5 to 10 minute to stop moving. I found if I use a cup and leave it in there I get different readings then just the tank. I'm guess residual minerals or something affects the ph.
I would just test your ph before co2 and after. Also run a air stone that previous night to make sure the c02 is all off gassed for accurate measurement.
I bought a calibration solution for my tds meter. Not sure if it's needed tds is just relevant to show change really.
Not to hijack, but I question the accuracy of mine too. Bought separate pH and TDS meters recently for about $32 total, so maybe I got what I paid for. But the pH meter doesn’t stop moving (in my case, lower over time), and though the TDS meter seems to show limited movement itself (like between 170-180 ppm) the temp thermometer it also happens to have is consistently reading 7-10 degrees cooler than the actual tank water temp (I have a temp controller and 2 quick-read thermometers and those three are always showing the same actual temp). So I don’t trust either meter.
Thank you @latchdan. I'll start testing for the pH drop. I just took some water out to give it time to degas. I won't draw any more samples for testing the tank water. I'll just dip the pen in the tank. I calibrated the TDS meter last night after posting and the aquarium water went down from 590 to 520 tap water went down from 390 to 320. The calibrating made it more accurate I think. I called technical support and they said my calibrating solution is the correct one for my TDS. The 2019 water quality report says the average TDS should be 276 ppm. Thanks for the response I've never used one of these before.

@mickmac, Are you testing the pH in the tank or are you drawing a small sample. My instructions say to draw a small sample but I think that's wrong when your injecting CO2. I envy your TDS of 170-180 ppm. I wish mine were that low. It is kind of suspicious how far off the temperature is. That TDS seems too good to be true compared to mine. I wonder if I should cut my water change water with 20% distilled water? I found a more recent water quality report:


There are five water processing plants. The Jensen Water Processing Plant is the one that serves my neighborhood. Just as a sidebar I recently tested the tap water for Nitrate and found 4 ppm. I used to test before water changes but now I test afterwards to better account for inputs from the tap water.

The CO2 is cranking at 5.6 bps and the drop checker is still green! I can't count bubbles any faster.
 

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@Savetheplants, Im testing with meters in tank water — turn meter on, stick into tank and swish it a bit, then hold the meter in the tank up to the “fill line” on the meter, then observe the meter reading until it stabilizes. Note, however, that I’m not (yet) injecting CO2 — maybe I should be testing in a drawn sample instead of in tank?
 

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Discussion Starter · #6 ·
@Savetheplants, Im testing with meters in tank water — turn meter on, stick into tank and swish it a bit, then hold the meter in the tank up to the “fill line” on the meter, then observe the meter reading until it stabilizes. Note, however, that I’m not (yet) injecting CO2 — maybe I should be testing in a drawn sample instead of in tank?
No, I think you're good. That's just lab procedure that doesn't apply to us hobbyist. I think we can disregard that "draw a 20 ml sample" instruction. At least when it comes to using a pH pen to test aquarium water.
 

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Some notes about care of glass electrode meters like PH meters. Before you use it, you must "wet the membrane" to use the old terminology. Most come with a cap. Fill that cap with 7.0 standard so when you close it the tip is submerged. Let it stay like that for 24 hours before you even start trying to calibrate. They usually come from the factory pretty close to calibrated. Do not store glass electrodes dry, or in DI or distilled water, it will cause them to function erratically.

You should have 3 standards, 4.0 7.0 and 10.0 - hydroponics ones work just fine and are cheaper than laboratory standards. Look at your booklet that came with meter for doing a 3 point calibration. Recal your meter before starting to measure for the first time. You only have to recal after this if your meter doesnt read 7.0 in fresh cal solution.

When youre going to take a measurement, flick the meter to remove any drops of liquid or give it a quick blot. Submerge the tip in what you want to test. It should only drift for a little bit, maybe 20 seconds before arriving at a number that stays. If you want to remeasure, take the tip out, flick it dry, then turn it off and on before remeasuring.
When you are done, blot it, and store it upright, capped with the 7.0 standard in it.
These tips will make your measurements much more consistent.

TDS meters can be stored dry, but also benefit from the off and on between measurements trick. There are saline standards of 342 TDS that can be used to check their calibration. The set screw ones must be adjusted Very gently, literally a wiggle will change your result by 10s.
 

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That’s interesting, @Dreya. The maker of the pH meter provided the 3 standards, but said online that initial calibration isn’t necessary because each unit is calibrated before shipping (which seems unlikely but ...). I also saw no mention of storing it wet! I’ll have to go back and reread I guess.
 

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Discussion Starter · #9 ·
Thank you @Dreya for the information about how to use the pH pen. That's very helpful. I plan on using the Turn it Off and On hack you posted about.

I took the TDS pen to the water store today to buy some water and told them there was 80 ppm TDS in there water. I tested their GH at 107 ppm last month. This was before I got the TDS pen. I asked him if he adds Calcium and he said no, electrolytes. They add electrolytes to make the water taste better. He told me TDS doesn't include stuff that's not dissolved. Well, I guess not. I've been going to this store for years and have been using the water to top off the tank. I called another store when I got home and they said they don't add anything. Eureka! Can't wait to test their water. I have to get my 520 ppm TDS aquarium water down to a more reasonable level. I'm going to order GLA Calcium Sulfate. I called LaMotte today to order their Calcium, Magnesium Total Hardness Test Kit. I have been skirmishing with algae lately. Maybe a lower TDS will help.
 
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