What causes algae to show up in my pond?

If the fish are staying in the pond, use only very low doses of formalin and be aware there is a risk of killing the fish along with the Ich....

Yes.

Buy some bottom-feeding fish that feed on algae and other contaminants to do the cleaning for you.

Yes you can. You could add watonai goldfish to your pond, as they look beautiful in ponds.

You could buy snails or shrimp, which will eat the algae.

Yes, but you need to prepare the substrate before fiberglassing the pond. It can be done by sanding the surface and washing the surface beforehand.

Typically, 12-24 inches is the final depth for water lilies, but the starting depth is 8-12 inches underwater.

Some rocky material tends to do really well with a pond. Pick up boulders in multiple sizes to add some variety. Depending on the size of the pond, start with...

Install an aerator, waterfall, or something else that is able to keep the water moving. Mosquito larvae require non-moving, stagnant water to thrive, so anything that keeps the pond water...

Only if you need them out of the pond for one reason or another. If you are okay with them in your pond, let them be.