"In chemistry, pH (potential of hydrogen) is a numeric scale used to specify the acidity or basicity of an aqueous solution."---wiki. Ie, is your water acidic like lemon juice---or alkaline like a desert pool?
On that scale, battery acid (ph of 1) and drain cleaner (ph of 12)---both extremes can burn.
Your tank should be between 7.9 and 9 for the comfort of fishy skin and gills.

BUT--- ph in a marine tank wanders all over the map during a given day. Pretty...

The Users' Guide to Green Hair Algae
[a companion to the cyano thread]

Green Hair is actually tougher to get rid of than cyano---because it pretty well WILL run its course in a tank.

But it's a pretty straightforward algae. It loves phosphate. It grows like mad in a new tank.

A lot of new people, hearing the bit about phosphate, run out and get a phosphate test. This is pretty useless for the green hair algae period of a tank. Of course you have...

Understand, you can run a very simple kind of 30 gal tank with nothing but a pump, a heater, live rock, regular tank light, and a Penguin filter, with a 'fill line' drawn on the glass to help you top off accurately with ro water from the supermarket. This is the ancient method. It will support a few crustaceans and snails and a couple of very small gobies or blennies or dartfish.

If you want more than that, your problem becomes too much nutrient in the system, not enough waste removal,...

Four 110 watt VHO UVI super actinics powered by Icecap 660 ballast.

Four Lumenarc III 20"x20" reflectors.

Four Radium 400 watt 20,000 kelvin on two Sunlight Supply HQI ballasts.