Welcome
Well you've got yourself some pea soup...but do not despair !
@sissy is correct, some shade, more water circulation , pond plats and aeration will all help.
We have a shade sail over our pond. Do you have anything to attach a shade sail to ? They're pretty cheap, we got ours at Costco. Also a patio umbrella would help....or rigging up landscape fabric on poles.
A lot of us like
https://webbsonline.com They have a good reputation and fair pricing. You can order online , which frankly is how a lot of pond business is done these days with fewer pond brick and mortar stores around. Take a look at the aerators and pumps / filters.
Look into ordering some floating pond nets or make your own with nylon window screening , pool noodle and zip ties. If you can't find water hyacinth, water lettuce or other floating plants....trying looking for water lettuce and water celery in the produce section of your grocer. Also, I've had very good luck growing impatiens in floating nets.
Depending on the depth of your pond you could set pots of hostas and elephant etas in the pond. I am mentioning these plants in case you have trouble locating pond plants.
Don't despair, gold fish are pretty hardy fish. STOP the algaecide treatments at once and read up on the "nitrogen cycle". Make sure you use a de chlorinator if you use city water treated with chlorine. Also, invest in an API water testing kit.......test for ammonia, nitrite and nitrate. From the looks of your pond I bet you have high phosphates too.
Again, welcome and do not despair