Ideal pH range for our aquarium plants and critters is between 6 and 8. In this range most aquarium plants, critters and microbes are accustomed to live. If you create an environment that is outside this range, you can be quite sure that it will not meet their needs. Ignoring this principle means ignoring the fact that all living creatures are different (in a way), and has a different demands. Some plants thrieve in higher pH, while other may thrive under lower pH. Some plants have affinity to free CO2, while other have affinity to HCO3. Some plants prefer the nitrogen in NH4 form, while other plants prefer NO3. If you study plant physiology and ecology, you would know that.
So ask yourself the following questions:
- What environment is optimum for nitrifying bacteria?
- What environment is optimum for your plants?
- What environment is optimum for your fish and shrimps?
Some facts:
- Nitrifying bacteria are most effective under pH 7.2 to 8.5. At pH 7.0 only 50% of nitrifying bacteria are active. At pH 6.0 only 10% of these bacteria are active, and under pH 6 most nitrifying bacteria stay dormant and cease to multiply. PS: The there are great many numbers of bacteria in our tanks, and nitrifying bacteria are just a very small part ... so the pH doesn't affect just the nitrifying bacteria.
- While a great number of aquatic plants may prefer slightly acidic pH, not all will tolerate too low values in the long-term. Some aquatic plants prefer rather alkaline water (e.g. Vallisneria, Hydrilla, Ceratophyllum).
- Some fish prefer alkaline water with pH over 8 (for example, most Cichlidae species).