(Bi)carbonate equilibria in an aquarium

The carbonic acid / bicarbonate / carbonate buffering system is very important in an aquarium and largely controls both the pH and the resistance to change of the pH in the water. These three carbonate-based species can all interconvert in a connected equilibrium reaction: (1) H2CO3 (carbonic acid) ⇌ H+ + HCO3– (bicarbonate) ⇌ 2H+ […]

Reaching aquarium equilibrium pH

Absent active interventions such as injecting CO2 gas, having an ‘active substrate’ and the metabolic processes of fish and plants, the pH of an aquarium will equilibrate to a level mostly determined by the alkalinity of the water – the amount of externally supplied bicarbonate and carbonate ions. In most cases, “externally supplied” means came […]

Measuring alkalinity in an aquarium

NOTE: if you want to be really super-serious about measuring alkalinity you could consider instead the upgrade to this page: ‘Measuring low levels of alkalinity‘ The pH of water in an aquarium is a measurement of the concentration of hydronium ions H3O+ (or just H+ for short). Neutral water has a pH of 7, and […]

Alkaline aquarium water

Shrimphaus is [was] usually around pH 8.2 The Shrimphaus has an equilibrium pH of around 8.2 which is on the alkaline side. Chemistry and geology of Cambridgeshire water makes this the case, discussed below. Later note: Neocaridina can do ok in higher pH water, but Caridina not so much Chalk aquifers mean hard, alkaline water […]

Drop checker

A drop checker is a simple and reliable device for measuring the level of dissolved CO2 in aquarium water. The drop checker hangs from the wall of the tank inside the tank and completely underwater, e.g. with a suction cup, and contains a liquid with a pH indicator dye in the “drop” portion which is […]

Estimative index

“Estimative Index” aquarium plant fertiliser method and strategy The ‘estimative index’ (EI) is a fertilizer concept originated by Tom Barr where the general idea is to never have plant nutrients be limiting in the water column. Plants will grow and generally outcompete algae (so the theory goes). In practice, while I’m sure the outcompeting part […]