Clear pond?

Pond is more clear after it rains? How to keep it clear?

My house was built in the 50s with a koi pond on the front patio before koi ponds were trendy. There is no filtration or waterfall. The electric outlet outside the pond is broken. The only thing we have to filter the pond is a pipe in the pond that acts as a slow drain. There are 12 fish in the pond and they are very healthy. They've been there for 2 years and have had 3 babies. Even though I scrape the bottom of the pond for debris and skim the top once a week, the water is brown and murky. I add new water to keep the drain going and I use a water treater and a barley/health bacteria treatment. There is some minor algae build-up on the sides, but no plants. However, when it rained last week, the pond was clear for about 3 days. Why was the pond clear after it rained and how can I keep it clear?

I should clarify that there are 9 adult comet goldfish and 3 babies, not full-sized koi.

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  Read and heed this article that I wrote and you will have clear water. Feeding your fish is what is making the water murky.
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