Another filter hopefully the last, input appreciated.

[extra_g]

My pond is approx 600-800litres and am looking to building my last filter (famous last words).
Original was a tub and plants with a manifold feeding water from the bottom up through gravel, exiting close to top. Issues was no pre mechanical filter, it ended up doing more harm than good. Stank and collected sediment, not easy to clean as I buried it and no drain.
Then I went with a tall square tub, with the entry at the top, water had to travel through foam pads and some bio balls before travelling up a dip tub and exiting at the top. Again buried but easier to clean, removing the foam layers and rinsing them and using a cup to decant the water then repack and away it went.
The issue is that it is to much effort in cleaning.
So my next adventure with filtering is such.
I have seen UV stable stackable tubs at the hardware. I was thinking of a deeper tub on top of a shallower tub bellow.

OPTION 1:

In the top I thought of pumping the water in onto a screen mesh filter to remove the larger particles. The tubs are 600mm long so was going to utilise 300 for the screen and then on the other side drill a hole and let it fall into the biological filter tub.
Now in the lower tub I was thinking of starting with a wall of brushes then a vertical wall with holes in it (baffle wall) which goes into a section of filter pads. At the end put a solid wall which dictates the water level in the brush and pad section. After this wall the water will simply cascade over and exit via the outlet gravity feed back into the pond. Under the pad section place some air stone strips or similar running the width of the tub.

OPTION 2:

Same as option 1 but: In the top between the screen and exit to lower tub place a baffle wall then brush filters and a wall to dictate the water level in the tub.
Then in the lower remove the brushes and baffle wall and fill with mor filter pads and air stones.

Tub sizes are 600mm L x 400mm wide. Top is 270mm, lower is 150mm deep.

It is an outdoor pond and mostly get fine algae coming through to the filter, no large leaves. I am looking at ease of maintenance for this filter.


Do you think these options will work and if so which seems the better option?

For my screen mesh what microns do you think is best?

 

[LuckyDog]

Interesting... So how did you discover that the gravel-filled tub was getting manky? Did you first remove the gravel to have a look? Or did the water flow slow down?
I'm what you might call "invested" in this problem having a semi-buried tub with around 100 kilos of various gravels and no bottom drain. I have, however, incorporated a gutter downpipe with big notches cut out of the bottom edge, into which I can put a handheld pump (sold to pump stuff from the bottom of the pond - it works for that, at least) but haven't tried it yet because my gravel box is very recent and the fish aren't eating now.

 

[poconojoe]

Many of us filter exclusively with an upflow bog with fantastic results and zero maintenance. I don't know why your's failed. Some members have filtered with a bog for many years without any problems.

If it got clogged, maybe you were sucking muck off the bottom of your pond or maybe it was too small or built incorrectly. It's best to not sit your pump directly on the bottom where it can possibly pick up all kinds of settled debris.
I keep my pump off the bottom with a rope tied to it and anchored to a rock on the shore.

I will never go back to a filter where I have to constantly clean and rinse pads. It takes the enjoyment out of the hobby.

 

[extra_g]

So how did you discover

My pond was very, very green. I think it is referred to as pea soup. I had a hunch it was due to the filter so bought the parts and replaced the gravel tub.
When emptying the tub it was just not right, smelt bad, full of solids. After a few weeks with the new filter the pond was crystal clear.

It's best to not sit your pump directly on the bottom where it can possibly pick up all kinds of settled debris.

My pump does sit on the bottom but I have a PVC pipe attached that sits just below the water level and sucks the water from near the top.

Not sure why it did not work, perhaps it was to small. Unfortunately I am limited for space, I would love to have a nice large spill way full of plants acting as my filter but not possible.

 

[brokensword]

what PJ said. An efficient upflow wetland filter should not be fed by a pump on the pond BOTTOM as you'll for sure be pushing larger debris into the stone. A bog filter is a biofilter and not intended to be a mechanical one. So, that's the first issue to fix if you want to try again, which is what many of us here are going to recommend. Failures here with bog filters I can count on 2 fingers, yours being the second. Second issue might be you're pushing too much water too fast; the bacteria colonizing your bog stone need time to do their thing, so slow is actually better even though we have many reports here of more water and faster flows STILL working well. Third, you may have too much small gravel inhibiting the flow upwards, again probably because the flow is too fast or much. Can you give us a better outline of your failed bog design, the particulars? Maybe we can see something obvious.

I know this isn't directed toward your question, but when you KNOW a system works with NO maintenance (other than thinning plants periodically) and gives you more time to sit and enjoy the pond, you tend to want to encourage others to fix the design. Hope it helps just the same.

 

[poconojoe]

Even with my way way overpopulated pond, my bog still keeps the water crystal clear. And that's with a bunch of goldfish and a few very large koi. I think I'm up to about 50 fish in only 1800 gallons! Ridiculously overpopulated!

Before the bog I struggled with solid green water, and that was with two pressure filters and a UV running.
The water was crystal clear in less than a week after the bog build.

Something was not right with your gravel filter. It should have kept the water clean.
I don't know how it clogged up with your pump intake up so high off the bottom. There must have been another issue.

And, yes, as @brokensword has implied, you don't want the water to pass through the bog too fast.

 

[extra_g]

Something was not right with your gravel filter.

Looking at YouTube and how seeing how they are most commonly built, I can see why my filter failed.
It was to small, no false bottom, no access to clean, gravel size was not varied. I also noted that plants are not planted directly into the filter.
Unfortunately I do not have the space to setup a large enough gravel filter that will suit my pond.

I have ordered the materials to build my stacking tub filter so will see how it goes. I am hoping it will be effective and keep my pond crystal clear. The only thing I may add later is a UV lamp.