Heavily planted tank ph vs co2

[Joshua Boring]

We have a heavily planted tank using co2 injection. We have noticed that at night, the ph drops from 7.5 to 7.1/7.2

Is this normal?
Is this ok?
Should we shut down the co2 when we turn off the lights at night? Or just crank up our air stones?

As sensitive as discus are, this seems like a big ph swing.

Our kh reads 7 and gh reads 10

[AquaticNerd]

For a planted tank? That's normal.

For a planted tank with discus? You need to address the pH swings ASAP. while a .3-.4 pH drop may not be a big deal in the short-term, the long-term it will probably end up stressing your fish out. When lights are off, the plants don't consume CO2, so I don't see a reason why you would need to keep it running. When I've done planted tanks, I had the CO2 turning off about an hour before lights off. Your other and safer option would be the use a pH controller which can turn a solenoid on your CO2 setup off and on to maintain a stable pH.

[Adam G]

Brand new to discus but planted tanks I know well so I will share my experience. It is recommended that you turn off the Co2 one hour before your lights go out for the day and turn your Co2 on 1 hour before the lights go on. This is a starting point so you need to monitor PH and adjust from there.

It takes a while for Co2 to build up in the water so that is why the hour before lights on for the Co2. Plants tend to really benefit from Co2 as they start photosynthesis so getting some in the water column at the beginning of the light cycle is beneficial. They will use Co2 and release Oxygen during lights on. Being you are shooting for PH stability you may want to try 20 minute before lights on and see how it goes.

After lights out they actually release Co2. So stopping Co2 before lights out is recommended. They will continue to release Co2 for hours after lights out so this will keep PH stable at night. You will need to experiment based on amount and type of plants, and amount of Co2 dosed, every tank is different.

Lastly I have learned that a ton of Co2 is not necessary for a thriving tank. 20ppm is more than enough. 30ppm is considered ideal but getting this level of Co2 will significantly swing PH. Tons of great info out there on all of this as well. Here is a great resource that I have found very helpful. Read through this entire site and you will have a full understanding of all of these principles.

https://www.advancedplantedtank.com/

[Shan_Evolved]

Now this I have tons of experience with. I've had a 75 planted tank with a flourishing amount of red plants and carpeting. I had co2 injection through a sera reactor pumping out close to 40-50ppm or yellow on my drop checker.

For CO2, turn it on an hr and a half before your lights turn on, and turn it off 1 hr before they shut off. When it's nighttime the plants release tons of CO2 into your water, so you need to combat that by having powerful bubbling aeration in your tank at night to dissipate the CO2.

I also learned the PH change due to CO2 levels fluctuation aren't as bad as having a standard PH swing, though you should be careful regardless. With a KH of 7, your PH shouldn't be swinging that much normally, but of course in this case we have CO2 injection, just need to fine tune it.

I would

-turn on CO2 1-1 1/2 hr before lights on
-turn off 1-2hrs before lights turn off
-run a lot of airstones at night.

As far as running airstones at night - you can always measure your PH levels per hour once you have the airstones running and youll see that within a specific number of hours your PH will stabilize. For my 75 gallon tank it took 4 hours for my PH to go back to neutral, so I only ran the airstones on a timer for that amount. Though there is no harm in running all night, just make sure you turn them off before CO2 turns on.

Then again you can always leave it on as more oxygen is really important for both plants and fish. Planted tanks are so challenging in that you have to figure out the balance of CO2, Oxygen, and growth

[Joshua Boring]

Any recommendations on a ph controller/solenoid? Sounds like something I’d like to try

[AquaticNerd]

A little pricey, but this Pinpoint pH Controller allows you to control via standard sockets without having to get special converters, etc.