Rise and fall of pH

[Jaap]

Hi,

I have a low maintenance planted tank with a spray bar that agitates the water surface for better gas exchange. I also have a Seneye that records the pH of the water. I have noticed that at night the pH rises and during the day it falls. One would think that during the day where plants photosynthesize, use up CO2 and thus the pH would rise and during the night where plants release CO2 the pH would fall. The opposite happens though and I cannot explain it.

Any ideas?

Thaks

 

[zozo]

That's what happens in my tank, also have a permanent pH probe in the sump, the pH drops 0.3 units during lights off and lights on it takes about 2 hours to rise 0.3 units again. This is pretty consistent sometimes it's 0.4..

Other way around is indeed odd.. No idea what the cause could be..

 

[darren636]

.microbial activity?

 

[ian_m]

That's what happens in my tank, also have a permanent pH probe in the sump, the pH drops 0.3 units during lights off and lights on it takes about 2 hours to rise 0.3 units again. This is pretty consistent sometimes it's 0.4

Electrical interference from lights and/or pumps. pH probes, especially cheap ones (say below £50) are very susceptible to electrical interference and leakage currents in the water. Try taking pH measurements at different places in your tank/sump and measuring with all other electrical items unplugged.

 

[darren636]

My tds meter reads much higher with the tank lights on.

 

[zozo]

Electrical interference from lights and/or pumps. pH probes, especially cheap ones (say below £50) are very susceptible to electrical interference and leakage currents in the water. Try taking pH measurements at different places in your tank/sump and measuring with all other electrical items unplugged.

It a Hanah instruments GrowCheck, the one with 2 probes, anode/katode.. It's actualy the most stable checker i have in my collection. Not susceptible to interference.. It's placed bellow the tank in the sump, the lights are over 3 feet above it. If i disconect all electrical equiptment in the sump the pH doesn't change a bit. It also doesn't change instantly when lights go out, i'll just notice in the morning the pH droped over night 0.3 units and during lights on about 2 hours it back 0.3 up again. I suppose it's the tiny co2 drop the plants use.

 

[dw1305]

Hi all,

I also have a Seneye that records the pH of the water. I have noticed that at night the pH rises and during the day it falls.

Is it low conductivity water? If the water isn't hard and salty the Seneye probe won't give you an accurate reading. There is a thread, "Rise and fall of pH....">

Electrical interference from lights and/or pumps. pH probes, especially cheap ones (say below £50) are very susceptible to electrical interference and leakage currents in the water. Try taking pH measurements at different places in your tank/sump and measuring with all other electrical items unplugged.

That would be my suspicion as well, pH probes measure electrical charge.

There is a good explanation here <"Practical pH theory....... ">.

When the pH probe is inserted into a tank, the readings can fluctuate wildly or provide generally unstable results. This is typically due to electrical interference from a mixer motor or some other device grounded through the tank. Remember that the pH signal is only measured in thousandths of a volts. It would only take a small transient voltage to be the cause of interference.

cheers Darrel

 

[darren636]

Hi all, Is it low conductivity water? If the water isn't hard and salty the Seneye probe won't give you an accurate reading. There is a thread, "Rise and fall of pH....">That would be my suspicion as well, pH probes measure electrical charge.



There is a good explanation here <"Practical pH theory....... ">. cheers Darrel

Darrel,
What's the best method for measuring pH in a very soft water fry tank?

 

[zozo]

Yes i also have a Milwaukee, which only uses a single probe the glass one obviously without a ground pen.. This one goes totaly crazy when something with an electrical field around it comes near. I have a little mistmaker which works ultrasonic, when i put this in the tank the milwaukee goes on error.. And the Hanah with the extra ground pen stays rock steady.

Ph meter measure volts, the gel fluid in the glass ball has a steady known conductivety an it recalculates the conductivety difference from the water it is in.

Also did read that 2KH and bellow PH can be inacurate..

 

[ian_m]

What's the best method for measuring pH in a very soft water fry tank?

A better quality (3 electrode ?) probe. Or harden the water first. Some cheap probes (notably from China !!) won't read reliably below 8KH, as stated on their instructions, but in my experience 4KH is usually the limit.

 

[dw1305]

Hi all,

What's the best method for measuring pH in a very soft water fry tank?

There isn't really an easy one, mainly because pH becomes less and less biologically meaningful as you approach pure H2O.

Solid state ISFET pH meters are better in low conductivity solutions, but they are expensive.

You can try adding a <"neutral salt"> to a water sample drawn from the fry tank, ordinary salt (NaCl) is the usual one, unfortunately you can't use "table salt" because it has magnesium carbonate (MgCO3) added to it. Potassium nitrate (KNO3) is another "neutral salt" option.

The salt won't effect pH, but it will raise the conductivity of the water, allowing you to get a measurement.

Personally I don't try to measure pH in low conductivity water (I just measure conductivity), once we are below ~100 microS I know that any introduction of weak acids (like the tannins from Oak leaves) will reduce the pH.

cheers Darrel

 

[zozo]

For anybody experiencing interference i solved my interference problems with the milwaukee like this. That's why i actualy totaly forgoten about having this issue in the past.

Put it in line, away from the tank and any disturbing sources comming close like cell phones.

Sometimes, probably a diet thing and or certain polyester fiber (fleece) sweaters, my own static charge caused eratic ph changes when sticking a hand in the tank.
Since it is inline and nothing comming near it, it's steady..