The difference is that Alkaline Buffer is a carbonate/bicarbonate based buffer and Alkaline Regulator is a phosphate based buffer. High phosphate levels can promote algae growth so it is often a better choice to use a phosphate free buffer like Alkaline Buffer. The only drawback to a non-phosphate buffer is that there tends to be more pH fluctuation owing to CO2 equilibrium. Phosphate buffers lock the pH in quite well and hold it there.
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