Help with pump spec

[allgood79]

HI everyone, been a while since I last posted but have been keeping up with the threads!

I'm after a little help for a pond that my dad is building in his garden, he's built the pond itself (2500 litres) and is just constructing a bog filter that I talked him into doing, we drove around a couple of fish places this weekend but they were little to no help really - we are struggling to see what size pump he is going to need, I'm not sure what effect the gravel/bog filter has on flow? His pond is two feet deep and the bog filter is probably half a foot above the pond. When we asked at the shops we got answers ranging from 2500 liters an hour to 8000 litres an hour! I know the old saying that you can "never have to much flow" is common but, to me, 8000 litres an hour seems excessive for a 2500 litre pond?

Anyone have any thoughts? Any help would be appreciated! Many thanks.

 

[combatwombat]

Kind of depends on how many fish you plan to have. I've heard they like to multiply so good to overshoot that. For your size pond + average fish density, I'd shoot for 5k LPH. The bog will probably need quite a bit less flow than that, and the way to address that is to install a wye fitting on the line from the pump. Send a slow flow to the bog (10 min dwell time in bog is a good target) and dump the rest on top of the bog or send it to another waterfall.

Pumps work best in the middle of their curve, so you will probably need a pump rated for a bit more than 5k to get best performance from it. Every pump should publish a pump curve, so calculate your total dynamic head (height between water level and output of pump + friction loss from piping) and look for a pump that will get 5k at that head height somewhere in the middle 2/3 of the curve.

Does that all make sense?

 

[brokensword]

an addendum to what CW noted; I like to have more than one pump for redundancy's sake; you don't want to have to wait for a new pump to arrive if yours fails. So, I'd say get two that cover the 5k lph spec you want. Or at least have a backup planned/waiting.

 

[poconojoe]

You don't want to force the water to flow too quickly through the bog. It needs to be a bit slow so the solids can settle and the plants have time to extract the excess nutrients.

If you feel it's flowing through too much, you can divert some of the water in another direction back to the pond or over a waterfall.
Some do this with either a diverter valve or a wye fitting with two valves on each outlet to custom control each one.

Run it with just the one line and see how it goes. It just might and probably will be OK. You'll always have the above suggestion if need be.

Mine has a 3600 GPH pump going through 20 feet of 1-1/2" flex pvc, then changing over to 2" pvc in the bog. The bog has two 10 foot lengths of 2" pvc as a manifold.
The flow has been good and the water is amazingly clear, even with way too many fish. They just keep multiplying! Is there a way to neuter these beasts?

 

[addy1]

The flow has been good and the water is amazingly clear, even with way too many fish. They just keep multiplying! Is there a way to neuter these beasts?

NO just don't feed get them to snack on the eggs...................or build a bigger pond!

 

[poconojoe]

NO just don't feed get them to snack on the eggs...................or build a bigger pond!

Yeah, I think I'm going to use that advice about not feeding them much once the eggs come.
They haven't started that relentless chasing of the females just yet. Maybe soon.

 

[mrsclem]

I stop feeding for at least 2 weeks. Eggs eaten first , then fry!

 

[jmajid]

i just saw my koi started....

 

[addy1]

Yeah, I think I'm going to use that advice about not feeding them much once the eggs come.

not even as much try not at all

 

[allgood79]

Thanks all for the comments, much appreciated! Time to hit google and look at some pumps! lol