When you say “replaced,” do you mean by periodically draining and refilling? Some people do this — it’s called a “partial water exchange” (because not all of the old water goes away). However, many don’t. There are different schools of thought on this issue. But if Mother Nature doesn’t do it for us in the form of rain, we pretty much all top off our ponds as the water level decreases. That is, “replacing” what was removed via evaporation. You said you’ve not replaced any water in over 10 years. I hope you are topping off the pond (unless it’s a spring-fed pond).
Sludge removal also has different schools of thought. Personally, I like to remove the sludge if it gets bad (“bad” being a personal choice — there is no standard for what “bad” means) but if you do that you can get it out with a fine net — the water doesn’t have to be emptied for this. But be aware that when you stir up the sludge, it will release potentially toxic gasses into the water, so keep your Pump and filter running and add some extra aeration if possible. Or, if you have some type of pond vacuum, that works well, but you’ll still stir stuff up. I have a Pond-o-Vac that gets used about once a year. Oh, and sludge removal can also depend on trees and how much leaf-drop you get.
Hope this helps!
