So the trade-off with pressurized and gravity fed then is size and costs, right? A gravity fed one, for about 1500 gal pond, would be pretty large but the cost to run a pressurized one could be quite high (because of the need for a stronger pump).
Can be true, doesn't have to be. A fluidized bed isn't pressurized and is a state of the art bio filter and smaller than any other filter for the same bio load. Years ago pressurized filters were more common as bio filters. Now days I think they're only used for mechanical filters as a final polish (sand filter) or as a pre filter (bead filter)
To me pressurized means like more than double the pressure in an open pipe and also that the pressure would increase as the filter clogs. All these have some pressure of course.
Maybe I am trying to make things more complicated than they are -or- I am looking for the 'right' way when there are, in fact, many right ways.
Every pond is a custom job. Plus it's a bit surprising how fast the state of the art has changed. When I started the state of the art was an up flow gravel filter. Then submerged media, then bead, then trickle tower, then shower, then fluidized bed, and a few dead ends in between. Water garden techniques on the other hand stand still, completely unchanged in 15 years except maybe for better scams like barley straw to barley pellets to barley concentrate.
Here is an example...you mention to put the BD outflow pipe at about 1/2" below desired water line but, up above, in Whisky's drawing he shows the line entering the filter box at about mid-level. Now, I may be reading too much into his drawing and it is just showing that the connection is made and not to imply at a certain level. If it just does not matter if the DB drain enters the filter box at the top, bottom, or middle, then that would be a perfectly acceptable answer also.
Correct. I personally don't like to run the pipe thru the filter wall when DIY. It's more work, can leak and it can be a tight area to work in. I like the pipe to just dump into a sieve/filter/box. In my case the top of the filter is below the water line and would flow by gravity into a body, like the small pond, at the same or lower elevation. So the box doesn't overflow.
psst...I'll give you a little insight into my mind...I am a computer programmer by trade and an engineer by nature so I have a propensity to need to know and understand the details. that's why a high/mid/low level question is important to me. I don't mean to be a bug about those details - that's just the way I figure things out... So, I'm a details main. I want to know the details and, if it is going to get done, it will be by me and not hired out as I am a big DIYer when it makes sense.
Same here on all counts. I'm suppose to be coding instead of being here.
By using a smaller pond, what you are saying is that then the main pond will always be at 1 level...that makes sense. Although quite possibly not an option for me I am intrigued by the idea and need to go learn about that.
Yes, main pond is a constant full level. The look is great too as you never see water line marks on the sides, always looks full. I'd never do a pond another way.
Use the filter as the "small pond"...
So lets talk details...keeping in mind what Whiskey said a few posts back...when you turn on a pump it starts drawing down the water level in whatever box it's in. It takes some duration for the pumped water to fill pipes, streams, pond, whatever, and overflow back into the pump box. Say it takes 60 seconds and the pump is drawing 1000 gph, the pump box will draw down by about 17 gal. So the pump box would only need to be say 30 gal and it could act as the "small pond".
That all assumes the main pond, streams, etc are already at their full level. If the pump as been off for a day the main pond could be down by 100 gals by evaporation in which case the pump box would run dry. So it takes a bit of understanding. But then you know to top off the main pond before starting the pump.
Even if the pump box isn't big enough a garden hose can be run into the pump box to add water as the pump reduces volume. Gives you a bit more time. The down side is if the pump is turned off the pump box would overflow. But generally the pump runs 24/7 so not an issue.
The other issue is evaporation...it all accumulates in the reservoir (small pond or pump box). A small pond could go maybe a week before running dry while a 30 gal pump box might be dry in a day or two. That's fixed by putting a float valve connected the home water supply inside the reservoir. I supply the float valve to an automatic sprinkler valve on a timer as a backup since float valve to fail.
So the size of the "small pond" reservoir can be very small. All depends on the main pond surface area, stream, etc.
Drip water changes...
One more thing I'd throw in...something I've never done before but will on my next pond...drip water changes. Normally water changes are where you drain out some amount of the pond, 10% or 20% and fill with new water. There are a lot of issues with it, temp, pH, chlorine. The drip change is done with a drip emitter that is left on 24/7. So a 1 gph emitter would be an 11% change per week in a 1500 gal pond. At 1 gph you don't have to worry about chlorine, pH or temp issues and you never miss a water change.
I'd put a regular hose bib thru the pump box below the water line. I could run a hose from the bib to the garden to water plants. I could measure the amount of water coming out of the filter with a bucket and stop watch. Once dialed in I can forget it. And the auto flow would keep things topped off.
I bring this up because it ties into the pump box water line deal. I'd have to make sure the hose bib was above whatever in the garden I watered. With a raised pond it would be no big deal. An in ground pond, in a flat yard means I'd have to be really careful. Then again, I guess I could just put the bib in a pool in the waterfall. Either way, had to be thought though.