Hi Joe!

You are running about 950 gallons in what looks like a fairly sunny location. Your fish load is appropriate for the volume, and as long as all you have is goldfish, your filtration is probably sufficient as well. Koi, even only one or two, would rapidly overstress your system.

Your problem is algae, a product of warm, phosphate-rich water, ammonia from your fish and sunlight. The hair algae is going to be a problem until you can establish robust verge plantings of semi-aquatic and aquatic plants in your rocks. These will need to have their roots in the water, and will need a year or two to become fully established. In the interim, a brush on a stick is your best solution.

The rest of the cloudiness and sludge is microscopic floating algae, and the best solution for this is a small high-intensity UV unit placed in line after your prefilter. This will keep the algae from reproducing, but will not add to the organic load in your pond. Algaecides will kill your algae, but in so doing will increase your organic load and degrade water quality.

UV units for your size pond are inexpensive and easy to maintain.

Happy ponding.

Bob