The rule of thumb is to have a pump that circulates the entire pond every hour, so a 500 liter pond should have a 500 liter/hour pump. From what I can find out, your pump is a little too big, but to big is easier to deal with than too little, especially if you want a waterfall or tall fountain.

Thanks T,. I have a waterfall and a small fountain ( too big and it blows out of the pond ). The filter I have in now is quite old and I got this for a bargain price but am beginning to wonder if it will turn out to be a bargain or a white elephant ? :0))

Well...it will use more electricity, and burn out fast if the filter can't keep up the flow.

If the filter isn't sealed it will just leak if it can't take the flow, and the pond water will be lost onto the floor. You should be able to get a bal valve to put on the outlet from your pump to control the flow going to the filter - I have an Oase aquamax and that's precisely what our setup is. The ball valve keeps a decent flow going into the first filter tank (made from and old cetral heating cold water tank) which is filled with brushes and faom. From there it exits into tank two (a smaller cold water tank) which has the media for the bacteria to live in to denitrify the water. Thie water exits this tank and down a stepped waterfall back into the pond. It has run like this for years now keeping the water in top condition. The only thing that stops the pump is when a bit of gravel too large to pass through gets stuck in the impeller.

You sure about water volume Valadel? A pond a metre square and only half a metre deep would give you that sort of water volume thats really very small to have a waterfall and fountain in .

As Tug says dont worry too much about pump size they are maximum guides and most important if you have a long distance from pond to waterfall and a high waterfall drop ie more powerful pumps required to pump water further and higher ..

Obviously the water is being recycled so when as your pump does , it says capable of moving 2500litres an hour it means your 500l water will move 5 times through that hour.Your waterfall is likely to have a very fast flow.

Some pumps allow you to turn off or disconnect fountain .. I would recommend this due to pond size as you ve already discovered fountains can lead to a loss of water and you d be forever topping up your pond.

I do hope the whole pond doesnt have to be circulated every hour Tug ours holds 28,000 litres ( 5,000 + gallons ) ..

Thanks Tug,Alocoloman and Bonkersbon have come to the conclusion its too big ( boo hoo ) as for the size B. it is 5ft x 4x 1ft in the middle ( only work in old money I'm afraid ) Pump too big , yes ? ?

Alocoloman: I usually set it up so the filter is "upstream" of the pump. That means that the pump is working harder if the filter gets clogged, but it's an extra hedge against stuff jamming the impeller. Of course, I'm also used to working with totally submerged systems.

Bonkersbon: The wider the pond relative to it's depth, and the more exposed to wind it is, the less pump it needs. The wind and convection will do more of the circulation work in a wide pond. I also just realized that I am using the figures we use here in the subtropical desert, where high water temps push more of the oxygen out of the water--so a smaller pump might still work. We also tend to shut the pumps off at night in the winter, so the water doesn't get so cold it puts the fish to sleep. Fountains are always shut off when not on display.

Valadel: Let me warm up my calculator...about 567 liters to your pond.

I have been reviewing the situation, ( there's a song there somewhere ) lol
Conclusion, ---- Its too big ! !
Thank you all for your answers, I do appreciate them.