Sorry to hear about the fish kill. School of hard knocks could have given you a light rap on the knuckles with a ruler, but instead you got a roundhouse kick to the head!
Your water quality does not sound good, but if the fish died that quickly, then they might not have been properly acclimated to the pond. (Which is even more stressful.)
Read up on filamentous algae in some of the archive threads. That way you will have the lingo and concepts correct when you ask future questions in the forum.
In most cases, a brand new pond is the low point for available nutrients to enable the growth of FA. From that point forward, the battle will become even more intense as the nutrients in the pond water slowly increase.
Unfortunately, there is no silver bullet. It will be a constant battle, that hopefully you will "mostly" win over the annual growth cycle.
One small tool is to plant some beneficial shoreline (emergent) plants and some underwater plants. They should take up some of the nutrients in the pond water, and thereby deny those nutrients to the FA.
Of course, you need non-invasive plants that are a benefit to your pond and the fish and other wildlife you are trying to support. I would suggest reading a few of the plant threads in the forum. (Of course, plants from one region may behave much differently in your pond if you have much different geographic conditions.) There are some beneficial shoreline plants that will make your pond (and your property) more attractive. For me, that is an excellent time to get input from my wife, since she certainly has a much better "eye" than I do, and you definitely score some husband points by making her part of the process.
What is the water source for your pond? (Probably either groundwater coming up through the pond basin, or surface run-off water.) If it is surface water, you may be able to do some projects on your property to reduce or limit the nutrients coming into the pond after rain events. Are you near fertilized farm land, livestock facilities, golf courses, heavily fertilized home owner lawns, etc.?
Finally, there are lots of FA experts on the forum. Keep posting questions, AND specific observations about your pond, and they will be able to give you some good guidance.
Congrats on your new property and pond! Hopefully, your family will get great enjoyment after you get your pond management running in the right direction.
