pH..........and why it may change (simple listing)

Here are a few of the most common reasons for pH Measurements Increasing or Decreasing.
The full science behind this can be quite involved, so I’ve just put main bullet points and brief notes rather than explanations on each point as to which way, or why, a pH value may change (that is a different thread althogether).


- Absolute Pure Water at standard temperature and pressure should have a theoretical pH of 7 (for all practical purposes)

- Tap water or any water subjected to the atmosphere is not pure water. But it may still have a pH of 7.

- A pH of 7 does not mean the water is pure nor does a pH of 7 give any indication of purity…..it simply mean the water has a pH of 7.

-Changes in Temperature affect pH.
The exact nature of the change depends upon the chemicals giving rise to the measured pH and to the method of pH measurement.

-Neutral Salts (such as Sodium Chloride) can affect pH and its measurement.
In freshwater, however, the effect on pH is quite negligible, but it may have a noticeable effect on electronic pH meters.

- Funnily enough, pH also affects pH (but that is something of little concern in a fish tank).

- Incorrect Measurement techniques will naturally give incorrect pH measurements.
pH measurements should be made at the same temperature; pH probes should be properly cared for and washed; test tubes should be properly cleaned between usage.

- Addition of Acids or Bases (or removal or neutralisation of acids or bases)
This is quite general and obvious what is happening when pH changes.
There are a number of reasons why a specific change in free acid or base occurs. Some of the reasons are interlinked….ie a cause may be compounded by another reason or pH control system.

- Carbon Dioxide will tend affect pH.
Carbon dioxide will also dissolve and be released from water over a period of time.

- Bog Wood, peat, etc will tend to affect pH.

- General waste may increase or decrease pH. Lots of rotting vegetation, for example, may produce organic acids that tend towards lowering pH.

- Calcium Carbonate rock (eg limestone, or coral gravel) will tend to affect pH (and also act within the pH buffer system)

- Inefficient Buffering.
Small changes in the amount of acid or base will cause changes in pH if there is no or very little buffering within the water.
If the water is adequately buffered at a given pH then the system will resist a change in pH if small amounts of acid or base are added.

- Water Softening or other water treatments may remove the pH buffering action of the water.

- Ammonia is a base and will tend towards increasing pH; but pH also affects the amount of free ammonia in the water.

- Ammonium is an acid and will tend towards lowering pH; but pH also affects the amount of ammonium in the water.

- Nitrosofication and Nitrification by biological filtration will produce acids (nitrous and nitric acid respectively)
If the buffering capacity is low, then the action of these biological filtration processes will lower pH (in softwater, these can lead to a ‘pH or Acid Crash’.)

- Photosynthesis by plants. Photosynthetic activity can affect pH.
If the water has a low buffering capacity (eg soft water) then the effect can be quite noticeable.

- You may notice a general trend of changes in pH between day and night (ie lights-on and lights-off….linked also to plant activity).

- Charcoal or other agents to remove dissolved chemicals may affect pH by removing acids or bases or other compounds involved in pH.

- Time…..well, time itself does not change pH but changes in pH when something is added or removed from the water are not also instant: some take a noticeable amount of time (eg some compounds take a long time to dissolve in water, or the gaseous exchange of carbon dioxide in and out of the water).

List?? Sometimes something is always missing off a list…..so if I’ve missed anything then please add it.

Ian

Thank God you kept it simple

christyg wrote:

Thank God you kept it simple

Was that OK?
It actually takes longer to do a simple list than it does to do the straight science (that why scientists do science as it means less work when explaining anything ).

ian

Jaysus nice one Ian,it's great when you don't go down the 'Science' route and say it in a way we all get,ehhhhhhhhhhh.

Ger

ger310 wrote:

Jaysus nice one Ian,it's great when you don't go down the 'Science' route and say it in a way we all get,ehhhhhhhhhhh.

Ger

Cheers Ger.

One thing that I hinted at on the list but forgot to emphasise (and it is important) is about the biological filtration:

not only can it lower the pH in tanks lacking good pH buffering, but it will also actually remove the pH buffering from the water itself.
That is where we see often see a tank not given water changes simply get more and more acidic OR having mad bouncing pHs until one day the fish pop their clogs.

Regular water changes is a good solution to that (and many other things).

Ian