Hi Guys, some advice. I presently run my CO2 via a solenoid, so it automatically turns off at night. Throughout the day my PH indicator turns a nice green colour which is all good, but overnight it goes back to blue and then takes most of the next day to go green again. Is this ok? Or would you suggest that the CO2 is left on all the time?
It would really depend on the current state of your tank.
There are a few camps:
1) Run CO2 all day
2) Run CO2 via a pH controller to maintain a certain CO2 concentration in the tank based on kH and pH chart.
3) Ensure maximum concentration of CO2 when lights turn on. <-- lots of people use this method.
4) Turn CO2 on ONLY during photoperiod. <-- Filipe Oliveira uses this method.
1) This is fine, it basically keeps your pH stable all day at a high concentration of CO2. My personal opinion is running CO2 at the concentrations that you want to run them at would be taxing on fish to expose them to it all day - especially if your dissolved oxygen levels are low.
2) The only issue with this method is that without proper husbandry/water changes/the nature of your tank (hardscape, almond leaf, buffering substrate etc) you will have acids leached into the aquarium. These acids will reduce the pH of your tank (and likely eat through your kH buffer) which will throw off your pH controller reading. Many people have success with this method - but in all of the tanks I observe, there tends to be algae - which is fine - but it suggests an imbalance in co2/ferts/flow for the light they have.
3) This would require you to "dial in your CO2 -- I use air quotes because this is often said hand wavingly because the process can be long and tedious. You would have to time your timer for the solenoid to ensure that the concentration of CO2 in the tank HITS maximum by lights on - in other words, your pH drop should be about 1 pH and your drop checker should indicate that you have a safe concentration of CO2 for your fish.
4) Just turn it on at a bubble count that gets a solid CO2 concentration -- I have no details on how FO does this - I just know he does. I suspect that he has a long ramp on the lights just to give the plants to turn on their receptors.
The reason we want CO2 at lights on is so that CO2 is a non-limiting nutrient; pair this nutrient with any methodology of dosing that you like, that ensures you have all the nutrients you need, and plants grow. If it is limiting, then your plants will struggle to grow (and we want to give them the best chance to) - when they struggle to grow and begin to die, they release nutrients into the water column - this is why most algae is attached to plants: it is a smorgosborg of nutrients for them