Help with pH/co2 levels

[ER Man]

100 gallon planted discus tank with sump(L60”xB30”xD18”). GHL 4 x dosing pump unit. 2 x pumps dosing 12mm of Macro and Micro’s per day. Co2 FE with solenoid controlled via pH. Controller. Lighting is 4 x TMC tiles on for 10hrs per day

Was originally changing 20 galls a week from a storage tank which is fed automatically via HMA filter, this water had approx. 6 grams of Potassium Carbonate added to it to increase the KH before pumping into tank as our water here is very soft (TDS out of HMA filter is 24) and approx. only 1 to 2 dKH. The co2 was working fine and indicator solution was Green – plants growing out of tank.

Have now, due to work load, have used the other 2 x pumps on the GHL unit to automatically remove 600ml of water each - every hour, and an auto water level fed directly from the HMA filter replaces the water. This gives a water change of approx. 35 galls a week

The problem I am now having is that the pH of the tank is sitting at 6.35 and very rarely comes above 6.5 so the co2 is not kicking in but the indicator solution is now Yellow with traces of algae in the tank.

So how do I get the indicator solution back in the green? Do I make up a solution of Potassium Carbonate and dose this via a separate pump? If so can anyone advise re the amount/concentrate to mix and dose? Or is there some easier way to do this. Thanks

 

[ceg4048]

Did you not specify that you are using the controller to control the pH? Well that means your controller is working if the pH is at a stable value. You need to add more CO2, so you'd need to set a lower pH. It's not really a good idea to use the controlling function of a controller. It's better to use it as a safety device to limit the maximum injection and to simply turn the solenoid on and off with a timer.

Adding K2CO3 to water cannot possible increase the CO2 of water. That just makes the water more alkaline.

Cheers,

 

[ER Man]

Hi ceg4048. The pH controller is controlling the pH, which is set to operate the solenoid when pH starts climbing to 6.5 This opens the solenoid and injects co2 until the pH reduces and cuts off. No Timer in solenoid circuit.
What I cant understand is that the pH very rarely climbs above a pH of 6.5 to inject co2. Therefor why is the indicator solution Yellow - to much co2? If I lower pH setting on the controller then more co2 would be injected which in turn reduces the ph to a dangerous level?
What I was meaning by adding Potassium Carbonate - was to increase Kh - making the water harder and increasing the pH so the co2 would operate. But Iam in a catch 22 situation as there is already, according to the indicator solution, which is new, to much co2 in the water? Iam looking for a way to stabilise the pH at say 6.5 while injecting co2 for the plants?
I hope this explains it better