PH stability.

The most common mistake in a marine aquarium that can be simply avoided fixed or noticed are PH fluctuations.
With out continually balanced PH you can not have ongoing success in a marine aquarium and virtually 50% of every loss of life in a marine aquarium is because of this.
With PH when the lights go off at night all corals and basic algae give off carbon dioxide and this one gas interferes with the balance between the base and acid which is where the Ph that you test for exists.
All algae, though manly basic forms, convert gases (such as co2, fosphates, nitrates, basicly anything other than just some nitrite and nitrogen) with the use of available ultra violet light into glucose as food itself (plus food for the coral if in a symbiotic relation ship with it), plus harmless carbons and amino acids to name a few, these once converted remain harmless in the aquarium and the algae give off some oxygen with in this process.

The released glucose can be destabilizing to the PH to some degree as it is converted by bacteria into ketons and alcohol and these are very good at destabilizing PH.

If you choose a tank with a small protein skimmer, very little current breaking the waters surface tension, you will loose life to the incorrect PH untested in your aquarium.

Just before the lights go on in the morning is the best time to test your PH to see if you will have a problem at some stage, this will show you what it is at its worst normally.

One way remains the best to keep all waters Ph stable and that is to cascade your water in the most violent manner out side the aquarium making sure the bubbles do not reach your tank water.

If in any doubt,all ways have some PH buffer on hand to PH buff your tank.