PH reading drop overnight

[teaklejr]

Hi. I have a 90 gallon newly setup planted tank. It has been running for 1 month. There is 1 large piece of driftwood, 2 smaller pieces, about 10 corys, 4 otos, 2 sae's and 8 cardinals. I have co2 injected into the tank for 8 hours a day, the lights are on for 10 hours and run a air stone at night. I have been testing all the levels and they are all fine except for my ph. During the day with the co2 on I am getting a reading of about 6.5 but in the morning when I check it it will have fallen to about 5.8-5.9. I have been doing water changes of about 1/3 every 4 days. I just don't understand why the ph reading falls like it is doing over night. My kh is 4 and gh is 9. The water is also cloudy which I assume is just from the tank going through it's cycling period. Not sure if I have a problem or just again the cycling period. Also I am using just tap water. Hope this makes sense and any info would be great.
Thanks

 

[VaughnH]

Are you sure your solenoid valve is working to shut off the CO2 at night? With no usage by the plants at night, the ppm of CO2 in the water should go up, driving the pH down, if the CO2 is still on at night. i"m assuming you don't use a pH controller.

 

[teaklejr]

Hi. Yes the solenoid is working and no I am not using a controller. I just checked it right now and there is no co2 being injected.

 

[Gerryd]

Hi,

Some types of driftwood will leach tannins into the water that will lower the ph even if they are not visible. If it is a large piece I can see this especially.

Re your cloudiness: What type/size of filtration are you running?

You should be running a filter that can turn over your tank volume at least 5-7 times per hour. This will also help flow and current which are important to fish and plants in many ways.

Hope this helps.