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  1. #1

    Nexus Level Issues

    Hi everyone

    New pond build. 5000L 1.2m deep with about 7m of 4inch pipe with a swept bend into Nexus 220+ from a Spindrifter bottom drain. Been running about 1 week now.

    Everything seemed ok until I had to partially empty the pond due to some leaks in the returns. Hopefully these have been fixed now. However, since then I have an issue where the pond level keeps rising as the Nexus keeps falling. I have to keep switching off the pump where the water will quickly (within a few seconds) resolve back to the correct levels.

    Both the inner and outer chamber of the Nexus remain the same level so I can only conclude that the pump is pumping out water faster than it is coming in. Whilst this doesn't seem possible, I have lowered the 10k variable pump to just 10% but the problem still occurrs albeit over a longer period of time. I cleaned the inner chamber and that also refilled from the bottom drain in a matter of seconds. So it doesn't seem to be the flow in. But what else can it be?

    If anyone can shed any light I would apprecaite it!

    Many thanks



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  3. #2
    Senior Member Rank = Jussai Alburglar's Avatar
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    Yes it seems like it's pumping out faster than its gravity feeding in, your 4 inch bottom drain shouldn't be struggling at 1000L per hour. My first guess would be that your bottom drain lid is too close to the floor and causing a restriction or something is stuck in the bottom drain or there is a restriction in your plumbing somewhere - is it 4 inch all the way into the nexus or have you stepped it down somewhere? Have you used a smaller pump fed rubber connector to the nexus, rather than a larger gravity fed one?
    Lid or blockage seems like the most likely suspect if it was working well for a week:
    Take off the bottom drain lid and see if the problem goes away.
    ...perhaps you knocked the drain lid whilst sorting out the returns?
    ... perhaps it wasn't on tightly and is sucked itself down a bit.

    If not you'll have to rod the drain
    Last edited by Alburglar; 14-03-2023 at 02:10 PM.
    2660 Gallons. 4" Bottom Drain and Skimmer. Draco Solum 16 Drum. Anoxic Filtration. Air lift returns.

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  5. #3
    If it was ok before you half emptied the pond and the problem only started when you refilled it, one possibility is an air lock in the bottom drain pipe. You can usually clear an air lock if you can purge the pipe with enough flow to wash it through so you could try that first as the simplest option. If that isn't possible, or it doesn't solve the problem, can you give more details of how the pipe is run and if there's a chance that the pipe makes a slight fall anywhere in the direction of flow?

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  7. #4
    Thanks for the replies

    It is a straight run of 4 inch to a swept 90 direct into the Nexus. No reducers.

    I did close off the drain at the nexus and pumped the entire contents of the Nexus into a paddling pool. I then opened the drain in an attempt to purge anything out. Nothing really came out. I did time the filling of the Nexus and knowing it is around 500L and it took around 3 minutes to totally fill, I calculated this would be around 10,000L per hour. I am not sure how accurate this test method is but it seems that there should be coping even with the pump on full. Idealy I was hoping to run it at around 30%.

    Since making this original post I have had it running at 30% and the level does appear to be holding but the Nexus is still 20mm lower than the pond height whcih still doesn't seem to be right.

    If it is the fact that I have put the drain lid down too low, is there a way of dealiing with this without actually getting into the water? I also don't want it popping off after either! Any tips on how to deal with this would be appreciated - as I am sure you have guessed I am a total newbie to pond building!

    Thanks a lot

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  9. #5
    I made the same mistake with my bottom drain lid .
    First time I had to get in and get my toes under the coping and try get my fingers under it . Surprisingly hard to stay under .
    It was pinned to the bottom. I've been really careful not to open the purge too fast since .
    This summer im going to get in and put some spacers under it or replace the stand pipe.
    No fun and now the pond is extra slimy

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  11. #6
    Extreme Koi Member Rank = Supreme Champion john1's Avatar
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    As said above sounds like the drain lid needs raising as 3 mins for the nexus to fill is a long time.

    I have done this a long time ago but a bit fiddly.
    Spread a ladder over the pond above the drain, now the drain gap needs to be about 1/2 ins,so I made two pieces of rigid drain pipe with a notch on the bottom to slide under the lip of the drain lid.
    Get yourself on the ladder over the top of the drain and lower the pipes down and under the lip of the drain opposite each other then wiggle the pipes up but go easy as you dont want to pull the cover off.

    I used two pieces of wood first but it is hard to lower them as they want to float.
    Hope you can understand all that worked for me ok as long as you can see the bottom.
    John

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  13. #7
    Thanks again for the helpful responses.

    What would the normal or expected fill time be for the Nexus? I read that 3500 gallons per hour is expected from 4 inch drains. This makes mine potentially a third slower than this figure but I do have a run of pipe of 7 - 8m which I guess will impede the flow.

    I kept the gap on the bottom drain relatively small as I do have a couple of babies in the pond. I don't think it would be much off 1/2 inch, if any, from the liner but under the lip there is the mounting ring/flange that raises it a little internally. Just trying to weigh up how much I would/could achieve in widening the gap.

    Probably drain the pond as I still have the paddling pool to pump the majority of water out!

  14. #8
    Its gotta be the lid.
    I think I've 9/10m run of 4" and haven't had an issue since.
    I like the ladder idea .

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