Raf

yeah, thats normal. New tanks will go through it. Try to use Reverse Osmosis or even better, RO/DI water for the tank and use a protein skimmer to help extract nutrients that would otherwise fuel the algae growth.

Depends... if you keep the fish in there while your cycling you'll need to do partial water changes daily perhaps (depends on test kit readings), to keep the ammonia and nitrite levels down. This will keep the fish alive but ultimately prolong the cycling of the tank. If you cycle with live rock only and no fish, you don't need to do a water change until after the cycle has completed and this is assuming you get enough rock to handle the future bioload. Water changes will be dictated by the stocking levels. Stocky heavy and you can expect to do larger and more frequent partial water changes. Stock lightly and do less water changes.

How long should I wait to do my first water change and what % for a 125 gal and how often? Thanks

Because the ammonia and nitrites (as the tank cycles) will be harmful to the fish, if they even make it at all through the cycle. It's not necessary to expose them if you're going to be using live rock anyway. Let the live rock cycle the tank.

I also have a sump/overflow system.

I do have a protein skimmer. Why is it bad to have these fish in here?

Hi - you'll need way more live rock to handle the bio load in the tank... Get the trigger and damsels out of the tank while cycling. Once the live rock has cured the cycle should be finished, may take a couple of weeks. 1 pound per gallon (or 2 pounds per gallon) should be a good amount of rock to handle the eventual bio-load of the tank. Look into getting a protein skimmer too.