Low ph and 8dkh

[ludlumjohn]

Hello,
I’m new to the forum. I have had planted tanks on and off for over 20 years and I’m suddenly at a loss with my current readings in my newly setup 350 liter tank.

I’m using Ada aqua soil (new ver.), I running c02 injection through a reactor and external eheim prof+ filter. I using a Chihiros pro 120 cm at about 65%. Also using pyrogen. Tank is about 3 weeks old and heavily planted. Up until today, no prior water testing other than a quality ph meter. My start ph was about 6.5 and I was getting it down to 5.8. I’m using RO and well water at about 75/25 well water. Other tanks that I’m just using well water runs about 8.0.

Today I used my Salifert KH tester and got a reading of 8.0dKH at a ph of 6.5 prior to c02. I’m confused by these results. If I look at the c02 chart for planted tanks that would put me way in the red zone, too much c02. According to this I should not be injecting more c02. I have confirmed these readings with strip tests and surprisingly they were very close. I have also as of today put a drop checker in the tank. So will curious to see how it reacts with the c02 injection. Currently other than heavily planted there are no fish. Actually just checked my drop checker and it’s green.

How is this possible?

Thanks in advance for your comments.
John

 

[hax47]

Hi,
A pH of 6.5 and KH of 8 would mean that you have CO2 levels above 100 ppm. if the drop checker is green, most likely some of the readings are false. Also, if you dilute your well water to 25%, you should have 2dKH in the aquarium, which, together with the 6.5 pH would put the CO2 at about 30 ppm.

I would check the following:
1. Make sure that the pH meter is two-point calibrated before the measurement. I would retest the calibration after measuring the water pH also (just put back the electrode into the calibration solution and check the pH)
2. Before measuring the KH, it is very important to rinse the vial with the test water multiple times with aquarium water. Remainings from the previous samples can alter the readings quite significantly.

I would not worry too much if the DC is right, most likely one of the pH/KH measurements is probably false. One additional, but unlikely option is that you have an excess alkalinity in water which increases the KH measured value but is not bicarbonate. Like phosphate, but you would need a really huge amount of that to affect the KH so much.

 

[ludlumjohn]

Thank you for the reply. I have reconfirmed all the testing via an alternate method and they are good. I did throughly rinse and clean all items prior to testing.
Just not understand how with those readings I would already have sufficient c03 without any being added.

I was thinking maybe the new aqua-soil was some throwing my tank off. Plants are doing fine and no sign of late yet. Just can’t make sense of the dkh and ph values

 

[hax47]

Just can’t make sense of the dkh and ph values

They do not make much sense unless the aquasoil is leaching some buffers in huge amounts, other than bicarbonate.
Do you measure the pH inside the tank? You may want to consider taking out the water from the tank for measurement. Some small electric currents (filters, pumps, heaters, etc.) can mess up the readings. Also, you may want to wait with DC readings a few more hours, it needs time to equilibrate. Check it the next morning, if it is green before the CO2 dosing starts.

 

[Andy Pierce]

Just can’t make sense of the dkh and ph values

Agree. That suggests that one or both of your KH/pH measurements are incorrect. Try turning off your CO2 and remeasuring your parameters. You should see the drop checker turn blue and the pH should rise and your KH should be unchanged (because CO2 injection does not affect KH). Can you give turning off the CO2 a try and report back how your drop checker / pH / KH values change?

 

[ludlumjohn]

As mentioned previously my drop checker was green before c02 was turned on. I will measure the ph out of the tank and see what I get.

Thanks

 

[LMuhlen]

As mentioned previously my drop checker was green before c02 was turned on.

Would you describe your tank as having good flow and surface agitation? Is it in anyway made airtight, maybe in an effort to preserve CO2?

It is well observed that one period of lights off is not enough to completely degass the CO2 even in normal conditions. It is possible that a configuration of your tank makes it even less effective at degassing.

This wouldn't explain the readings completely, but it would explain the drop checker.

 

[ludlumjohn]

Plenty of flow. Have a diy spray bar that covers the length of the tank with drilled hole to point over the surface without to much agitation along with holes drilled so water flows down the back of the tank. No covers. 🤔

 

[Hanuman]

See we have a fellow member from Thailand. Welcome.
Care to show us your tank?