I just wanted to share my understanding of reef pH which is mostly based on:
Low pH: Causes and Cures by Randy Holmes-Farley - Reefkeeping.com
Many would agree that reef tanks can be successful with pH between 7.8 – 8.5 NBS and daily swings as great as 0.5 NBS.
Natural pH levels in our ocean reefs are typically 8.1-8.2 NBS
pH/Alk/CO2 have a defined relationship. So given any two of these parameters, you can calculate the third. This also means that your pH is determined by your tank's CO2 and Alk levels. It should be noted that the addition or subtraction of CO2 does not impact Alk levels. So essentially, in our Alk stabilized systems effective CO2 determines pH.
A tank’s effective CO2 level is determined by CO2 sources (inputs) and sinks (outputs).
The main sources of CO2 are indoor CO2 levels and livestock. The main sinks of CO2 are photosynthetic organisms such as algae.
Indoor CO2 levels around a tank are typically between 600 – 1200 matm and can vary greatly throughout the day depending on # of people in the room/house airflow and the amount of outdoor air exchange. Outdoor CO2 levels are typically around 400 matm.
As an example, let’s say your effective CO2 level swings from 1200-600 matm and you keep your Alk stable at 8dKH. Your pH will swing from 7.85 to 8.12. If instead, you keep your Alk at 11 dKH then you’ll see your pH swing from 7.98 to 8.23.
In our small closed system tanks, it’s certainly possible to have much lower effective CO2 levels with poor circulation and/or heavy livestock stocking. Similarly, with heavy photosynthetic organisms, you can see much higher pH levels during the light cycle.
CO2 Scrubbers and high-pH additives (usually hydroxides such as Kalkwasser) can be CO2 sinks. It’s important to note that high-pH dosing effects are temporary as it results in removing a specific amount of Hydrogen whereas the CO2 sources (that increase H) such as your indoor CO2 levels will continually work to achieve equilibrium. Basically, pH buffers are very temporary (hrs) and add stuff that will eventually unbalance your tank. These are not good solutions for maintaining pH.
Calcium Carbonate reactors and low-pH additives can be CO2 sources.
Insufficient tank aeration will also result in CO2 accumulation in the tank.
A simple cup aeration test can help determine why you have low pH in your tank.
Methods that raise pH:
I hope this helps others. Please feel free to let me know if I missed anything.
Low pH: Causes and Cures by Randy Holmes-Farley - Reefkeeping.com
Many would agree that reef tanks can be successful with pH between 7.8 – 8.5 NBS and daily swings as great as 0.5 NBS.
Natural pH levels in our ocean reefs are typically 8.1-8.2 NBS
pH/Alk/CO2 have a defined relationship. So given any two of these parameters, you can calculate the third. This also means that your pH is determined by your tank's CO2 and Alk levels. It should be noted that the addition or subtraction of CO2 does not impact Alk levels. So essentially, in our Alk stabilized systems effective CO2 determines pH.
A tank’s effective CO2 level is determined by CO2 sources (inputs) and sinks (outputs).
The main sources of CO2 are indoor CO2 levels and livestock. The main sinks of CO2 are photosynthetic organisms such as algae.
Indoor CO2 levels around a tank are typically between 600 – 1200 matm and can vary greatly throughout the day depending on # of people in the room/house airflow and the amount of outdoor air exchange. Outdoor CO2 levels are typically around 400 matm.
As an example, let’s say your effective CO2 level swings from 1200-600 matm and you keep your Alk stable at 8dKH. Your pH will swing from 7.85 to 8.12. If instead, you keep your Alk at 11 dKH then you’ll see your pH swing from 7.98 to 8.23.
In our small closed system tanks, it’s certainly possible to have much lower effective CO2 levels with poor circulation and/or heavy livestock stocking. Similarly, with heavy photosynthetic organisms, you can see much higher pH levels during the light cycle.
CO2 Scrubbers and high-pH additives (usually hydroxides such as Kalkwasser) can be CO2 sinks. It’s important to note that high-pH dosing effects are temporary as it results in removing a specific amount of Hydrogen whereas the CO2 sources (that increase H) such as your indoor CO2 levels will continually work to achieve equilibrium. Basically, pH buffers are very temporary (hrs) and add stuff that will eventually unbalance your tank. These are not good solutions for maintaining pH.
Calcium Carbonate reactors and low-pH additives can be CO2 sources.
Insufficient tank aeration will also result in CO2 accumulation in the tank.
A simple cup aeration test can help determine why you have low pH in your tank.
Methods that raise pH:
- Keeping air around your tank/skimmer moving and well exchanged with appropriate CO2 level air (open windows, air exchange systems, outdoor air connected skimmers, CO2 Scrubber connected skimmers, etc…)
- Increase photosynthetic organisms in the tank such as macroalgae (Refugium with macroalgae running on a reverse lighting schedule will provide a boost at night to reduce common day/night swings)
- High-pH dosing such as Kalkwasser drip
I hope this helps others. Please feel free to let me know if I missed anything.