Any disadvantage to an over-rated pump?

Our pond pump has pretty well died - had a good look at it the other day and the bearings are more or less trashed. So we need to replace it.

The problem is that we inherited the pond (with pump, filters and fish) and don't have too much idea of how big it is. To complicate things, it's irregular in shape with 3 different depths. We can come up with a rough over-estimate of how big it is, but how far out it will be we don't know.

So, to get to the question, any suggestions as to how we work out what rated pump we need? And is there a disadvantage if we're generous?

Any recommendations for manufacturers that are good dealing with sediment gratefully received.

eta - it's currently got an Oasis Aquashift 3000, but whether that was fit for purpose or not I haven't a clue!

 

Hi Tangle the usual requirement the pond pump running the filter should pump 1/2 the pond volume every hour, Larger pumps would be needed for a heavily stocked koi pond,your pump is rated to run at 3,000 ltrs (660 gallons)per hour, you need to work out the volume of your pond to get an acurate figure, usually the oasis systems are sold as pump and filter together so the pump is rated to that size of filter.It would be better over than under size you could always throttle it down.

 

Thanks for that. Comes back to the volume of the pond, really, doesn't it. Are there any "soft" indicators as to whether the pump is sufficient? We won't be able to get an accurate volume (without draining it, which is unlikely at the moment), so having an idea of how to tell whether we've adjusted it right would be handy.

It's a bit of a weird setup at the moment - the output from the pump is split and half (ish) goes to each of two filters: one is an Oase Biotec 5, and the other I havne't a clue, but the water feeds through a UV lamp into a chamber with brushes and then into a larger chamber with lots of bits of pipe over a sort of gravel bed (looks like that stuff used to top the pots of plants in offices). Both filters return to the pond over a little waterfall.

On the one hand we suspect the pond is bigger than the pump should handle. But then again it's been in there at least 5 years, and most of the fish have thrived so it can't have been that far out, could it?

 

I agree with walnut, you should ideally pump the volume of water through the filters once every two hours, but no less than once every 4 hours.

The other thing to note is that not all pumps are the same. I will not go into great detail just now, but you do need a ââ?¬Å?filter pumpââ?¬Â, as these pump solids into the filter (as the pump you have does) so do not choose a ââ?¬Å?fountain pumpââ?¬Â as it will not be suitable

You are always better off getting a pump which is too big because you can always turn it down, you can not turn a small pump up.

Without knowing the exact volume it is hard to say if the pump you have is the correct size, and bear in mind that as you mentioned only 50% of the water is going to the main filter (The other 50% is going to the UV, although you also say it is going to a smaller filter)

Question, when did you last change the UV lamp? As these should be changed once a year, usually spring time (sorry if you knew that)

The diameter and any pipe bends / joints will also affect the flow rate, but I wouldn�t worry too much about it (but it�s a point worth mentioning)

You may find this click me pond volume calculator easier (direct to the page) sorry wiseoldowl

 

Tangle it seems to me the set up has been done by a pro. and if the pond is clear and the fish are healthy it must be ok replace the pump like for like the aquashift 3000 is a good pump as w g says it is the right type(they break up solids before feeding them to the filter)it's important to clean the flocculation brushes and chamber in the filter regularly as this bit traps the solids pulverised going through the pump but don't clean the gravel bed bit out,if you ever need to retain some of the detritus and put it back as this is full of denitrifying bacteria needed to keep the filter working correctly.

 

Personally if the previous pump seemed to manage I would replace with a similar pump. If you want to be safe and get something slightly stronger go for it. If you find it is too much you can always adjust the flow rate with an adaptor you get at most garden centres and fits directly onto the hose coming from the pump. You can't go the other way and increase it if the pump is too small.
Calculating your water volume is never an exact science when you bring in shelving for plants and variations in depths of water shelves and the pond not being exactly square etc.
Also the flow rate quoted by the manufacturer is the flow rate when plugged in and held at the surface with no hosing attached and no resistance. Drop the pump to the bottom of the pond add some hose and you greatly reduce the flow rate. Split the hose throw in a UV and a few bends and you decrease it even more. Without actually fitting a flow meter to the outlet and pumping through it for an hour you have no way of knowing the exact hrly flow rate. Draining the pond completly and fitting a meter to the hose and refilling will give you an exact water volume. This will however give you new pond syndrome and kill all the bacteria in your filters so not to be recomended Everything else is an estimate.
Basically it is best to have a slightly stronger or similar pump. Check water quality with test kits (Amonia, Nitrites, Nitrates) I doubt Oxygen levels are a problem with a waterfall. Base any further maitainence on the results from your test kits and either reduce fish stocks, improve filter media, increases / decrease water flow from the split in the hose to provide more / less water to the filter. You will get it right but if you had no major problems before then don't get too concerned about the size of the new pump.

John.

 

Hi folks (Tangle). I think it`s worth pointing out that it`s very important that the flow rate shouldn`t be excessive because the water , as it passes through the filter, needs a `dwell` time to enable to enable the filter to work effectively. I know that complicates things a bit Tangle....just thought I`d mention it. Cheers...freddy.

 

That is true, but you can always turn a big pump down, you can not turn a small pump up.

 

Hi. My point wasn`t so much about pumps but more the need to determine the quantity of water in the pond which will in turn determine the flow rate(this assumes that the correct size filter is in place). When the pond`s capacity is determined, then the correct pump can be put in place, taking into account the depth of water. You`re right in saying that you can restrict the flow of water, but, I`m not a fan of this idea because it`s bound to put extra strain on the pump. As for estimating the gallonage, I myself had an irregular shaped pond and being useless at maths I decided to try something else. Firstly I timed the amount of time it took to fill up a 2 gallon watering can, let`s say it was 15 seconds, therefore 1 minute = 8 gallons. Next I filled up the pond and made a note of the time it took. The rest is easy math . Tangle, if all else fails you could try this. Make a `guesstimation` and half empty the pond, then fill it up again using the method I`ve already mentioned, you SHOULDN`T be too far off. Cheers...freddy.

 

Seems I`ve killed this thread stone dead....sorry :(

 

on the other hand perhaps tamgle now has a pump?

 

We do now have a pump And the water is now clear (even bigger !)

Much dithering ensued on how big the pond was, but in the end we came down as somewhere about 4,000 L. Then there was more dithering on how much loss there was for the piping.

There are/were some weird things going on with the plumbing, though. For starters, the pump was connected to 2.5" pipe - but the smaller hosetails hadn't been removed. The feed that goes to the UV lamp T's off - the straight on option is still down 2.5" to the Biotec filter, and then the 90 degree tee to the UV is only 1". Based on OH's maths that means a seemingly meaningless amount of the water is actually being filtered by the UV lamp. We're quite tempted to disconnect it and see if there's any difference in water quality.

The plus side of the nice clear water is that the fish are very visible. The downside is that they're also very visible to any herons that come to say hello...

Anyhow, many thanks for all your suggestions. Fingers crossed it'll carry on coping nicely when the weather warms up

 

Hi Tangle. Assuming your pump is in the pond, the U/V should be fed directly from the pump then on to your filter before returning back to the pond. Cheers...freddy.