SimACo – PH/CO2 measurement and support

SimACo can monitor your aquarium water PH/CO2 level and control CO2 valve to keep aquarium PH/CO2 stable. For this purpose PH sensor and CO2 valve from CO2 bottle must be connected to the SimACo main board. You can use any PH sensor which has 50 Ohm BNC connector. This connector is a standard for most PH sensors. How SimACo controls CO2 level in your aquarium water? In the aquarium CO2 level and water PH are directly related through kH (carbonate hardness) parameter. kH value must be stable in the aquarium in order to get exact CO2 value from the measured PH value. If you know your aquarium kH and PH values, you can get CO2 value from these two parameters. So CO2 makes your aquarium water more acidic. This means that CO2 and PH is is inversely related: the more you dissolve CO2 gas in to the water the less water PH will be (water will be more acidic). You can use CO2/PH table to get required water PH value for the CO2 level you want to support.
Normally in a planted aquarium 30ppm CO2 value must be supported. SimACo supports two CO2 level scenarios. First scenario is to support required CO2 level 24 hours/day. This scenario helps to support aquarium water PH stable. It may be useful for some species of tropical fish. Other scenario: CO2 level is only supported at daytime; CO2 valve will be shut down at night. This helps to save CO2 gas. Plants do not need CO2 at night when aquarium lights are turned off. In this scenario water PH will fluctuate during 24 hours period. Also SimACo has inbuilt PH sensor calibration function because sensor must be calibrated every month to measure PH level precisely. For calibration two PH buffers must be used with low PH and high PH values.

Sensor calibration. PH sensor must be calibrated before using. To calibrate sensor PH buffers are used. You will need two calibration buffers: one buffer with low PH value and the second with high PH value. These values can be: 4.00 (4.01), 6.86, 7.00, 9.18 and 10.00 (10.01). It is required that high buffer’s PH value must be greater than the low buffer’s PH value by the 2 PH units or more. For example you can use 4.00 PH buffer as the low PH buffer and 9.18 buffer as the high PH buffer. But buffers with PH values 6.86 and 7.00 can not be used because the difference between the two buffers PH values will be lower than 2. There is a rule: the bigger difference between two buffers PH values the bigger accuracy you will get measuring with your PH sensor. So using of 4.00 PH and 10.00 PH buffers will be the best option. During calibration you will need to know calibration buffer’s exact PH value. Any PH buffer slightly changes it’s PH value according to the buffer temperature. Usually manufacturers declare buffer’s PH value at a 25oC temperature. But they also provide a table with buffer’s PH values at different temperatures. Calibrating PH sensor you must use PH values at a current temperature of the PH buffer. If buffer was in the room for a while you can use a room temperature as buffer’s temperature. For example: PH buffer has 9.18PH value at 25oC buffer temperature. But there is a 30oC temperature in your room, also buffer has the same temperature. Buffer at a 30oC has 9.14 PH value, so you must use value 9.14 during calibration.

Also there are two – low PH and high PH alarms implemented which will inform user that PH level is not normal.