Determining filter size and flow


info dump with tldr at bottom

I've got a sort of hot tub thing that's been left at the house ill be moving into in a few months. this tub is about 240 gallons (I think? circular 42 in 20 in deep). I want to know if a five gallon bucket filter with lava rock and filter floss would be able to handle the load from goldfish. Current plan is intake from pond->pump-> top of bucket->out of bulkhead from bottom side-> some sort of outflow like a rain bar. I've also seen a wide range of recommendations for pump size from half the size to ten times the size of the tank so I'm not sure what to do about that. I'm going to get a pond liner because their are jets and what not that I don't want to deal with. I've currently got a 10ft by 13ft one picked from some website calculator, I feel like this has to be to much.I see most pumps have 3/4 in fittings, is this really big enough to handle the necessary water flow?
  • is 5 gallons enough to filter a 240 gallon with fancy goldfish
  • is it 240 gallons 42in across 20in deep perfect circle
  • is intake from pond->pump-> top of bucket->out of bulkhead from bottom side-> outflow
  • how much pond liner do I need
  • what size pump do I actually need
  • do I use 3/4 tubing all around or should I use adapters to allow more flow with less pressure
I think that's most of it feel free to help where you can. one person does not need to answer these questions and I have several months before I even get started so chime in if you see this.

edit; I used the websites calculator and got 120 gallons, significantly different from the google calculator


For the pond liner size and volume of water for the pond there are many calculators on line. Use one of them. Just remember you will need a way to secure it on the edges like rock work or wood trim. Make sure with the calculator tour using the right thing. It’s either diameter or circumstance. Diameter is the entire length across circumstance is half the distance across the circle.
the 5 gallon bucket with lava rock and filter floss should be just fine. Do a foam block on the pump intake to prevent large debris getting intaken into the filter. Also find a way like a cut 5 gallon bucket lid to spread the water out over the lava rock to have it filter down through evenly.
Not sure what you mean by 3/4” tubing or adapters for better flow. Tubing without 90 degree turns will give you the best flow with least drop.
Filter size also depends on how stocked your pond will be with fish.
flow should be about 5-6 times the volume and make sure you account for head pressure drops.


Yes I came up with 120 gallons as well. I’m guessing you mixed up diameter and circumstance.


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