do you have fish, it would be hard to answer what is exactly wrong. Yes, planting around trees is never a good idea because they drop leaves, bird droppings, and in some trees, pollen. It's always best to have a pond away from those things. Also, if you live in an area where you have a great deal of wind, that too will bring a lot to your pond by blowing dirt, dust and debris into it. Make sure if you mow your lawn, to have a bag on the mower as that too will blow in. A filter is essential to help, also a way to oxygenate the water helps. Waterfalls are great, but only if they are really moving over the rock and churning up the water to allow that air into it. Fish are important. They help to balance the ecosystem. Some eat algae, some eat mosquitoes, some just eat food pellets, but most fish need an oxygen source. I agree that a pond contractor might be best for you, if you don't know about ponds or if need some help. Some might just come out and tell you what is wrong, and what to do to make it right for a fee. That will help if you want to do the job on your own.

stairs. I added a stencil border to mine.

paint before we repainted it several years ago. Then sprayed on a rust resistant product before the final color coats. I don't know if these chairs would stand up to sand blasting or not. Something to look into.