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CO2 Help


New Member
2 Aug 2022
Weston super mare
Hi All

Newbie here and having some issues with my CO2

Tank Dimensions - 120cm x 39 cm x 55cm - 240 litres
Fertilisation - EI Dosing with 50% weekly water change, dosed with prime
Filter Fluval - FX4
Filter Media - Ceramic Rings, Foam and Purigen
Skimmer - All Pond Solutions
PH Probe - Weipro
Powerhead - Yes 2000lph on right side above Filter intake, switches on during CO2 hours to distribute and increase surface rippling
Lights - 2 x 70w Twinstar 1200C
Light Schedule - 1pm-8pm - Both Lights 100% - 8-9pm - 1 Light Off - 1 Light 20% Power
CO2 - Yes via Fire extinguisher with Solenoid using a Bazooka Infuser - CO2 on at 9am - Off at 7pm
Substrate - Fluval Stratum
Hardscape - Dragon Stone + 1 Wood Piece
Temperature - 22-23 degrees at night and 24 degrees in the day
Dropchecker - Mixed with RO water + 4dKH solution
Plants - Cryptocoryne Undulatus Red, Micranthemum Tweediei Monte Carlo, Vericularia Montagnei 'Christmas Moss', Proserpinaca Palustris Cuba, Alternanthera Reineckii Mini, Eleocharis Acicularis Mini, Hygrophilia Lancea Araguaia, Lobelia Cardinallis Mini, Ludwigia Repens Super Red, Anubias Nana, Rotala Rotundifolia Green, Hottonia Palustris, Nylphoides Hydrophylla Taiwan, Hygrophila Pinnatifida, Rotala Macrandra, Pogostemon Erectus
Fish - Honey Gourami, Corydora's, Snow Plec, Zebra Danio, Hill Stream Loach, Cherry Shrimp, Amano Shrimp, Mix of Neon/Cardinal Tetras and Nerite Snails

I have removed some of the water from the tank and de-gassed it, shaking it within a bottle and leaving it overnight and the PH seems to be sitting around 7.56

My issue is the tank water at 7am (after switching CO2 off at 7pm) is sat at 6.65ph. According to previous threads we are aiming for a 1 point drop when the CO2 is on? Are we aiming for that 1 point drop taking into account the morning 6.6PH reading or from the fully de-gassed figure of 7.56 PH?

When the CO2 is turned on the probe currently drops to 6.2PH by the time lights turn on almost turning the drop checker yellow, the drop checker is still green in the morning when I wake up so I can only assume I am dosing too much CO2?

I have some Blackbeard algae forming on the corner of the glass where the silicone meets, could this be in part due to CO2 that is too high as I know I have sufficient flow and surface rippling within the tank

The plants seem to be growing very slowly, I'm not sure if it's impatience on my part of incorrect CO2, depth of the tank is too deep to get correct PAR rating from lights?


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11 Aug 2021
The calculation starts from the degassed (at equilibrium with the atmosphere) water sample. In your case this would be 7.56 .
In large aquariums it's often the case that there is enough inertia to not outgas all the CO2 during the dark period. This can be to your advantage as in the morning you reach that 1pH drop faster. With the plants density and diversity in the tank i don't see a need to push CO2 too much above the 1 pH drop. As long as that is consistent and you keep to the water changes CO2 will be good for now.

The setup looks rather new so I would give the plants extra time before expecting massive growth. BBA should be dealt with as soon as you see it. In your case I would drop the water level below the algae, put a clean toothbrush in some 'liquid carbon' and spread it over the BBA. Wait a couple of minutes and done. Repeat as needed. If the algae are too low to do that then either spot treatment or gently using the toothbrush to clean them and take them out with the water change.


New Member
Thread starter
2 Aug 2022
Weston super mare
That makes sense now. So I have actually been at a 1.5PH drop so will back it off till I hit the 6.5/6.6 mark

It is new, I stripped out my initial set up as I had a lot of hair algae and BBA. I believe this was organic material from the dragon rock that wasn't cleaned off properly. This new set up (water and filter already cycled) is about 2 weeks in. Appreciate the help on the BBA, thats exactly what I was going to go, use a syringe and basically does excel down the corners of the glass