Concrete Pond Construction

Q. A fellow nishikigoi enthusiast here said that for the pond of my size, 1 bottom drain is enough that feeds to the mentioned vortex, because having 2 inlets, the rotation will be too quick and the use of vortex is diminished because all the solid mass will not fall but over flow towards the other filters. However I am still skeptical.

A. The speed that the water will flow through the vortex chamber is decided by the pumping rate not the number of inlets to the vortex.
If you have one inlet and the pump is pumping at 2,500 gals/hr then that amount will pass through the one pipe.
If you have two bottom drains and still pumping 2,500 gals/hr then each pipe will pass through 1,250 gals/hr assuming they are the same length.
In both cases the amount of water passing through the outlet will be the same at 2,500 gals/hr.

Q. I have a couple of questions about vortex chambers. I am getting ready to build a new pond of about 8,000 gallons and plan to use vortex chambers to house the filtration system. I'm planning to use two parallel banks with three chambers in each. The flow rate through each bank will be about 2,000 gallons per hour. The first chamber in each bank will be settling tank. The suppliers of the vortex chambers list the maximum flow rate for each tank but do not mention what the optimum flow rate is. I want make sure the settling chambers will work effectively, so how can I determine what size to chamber will work best at that flow rate? Or is it possible that there is no ideal tank size because bigger is always better when it comes to vortex settling chambers?
My other question is how to best use the middle chamber in each bank. Assuming that the last chamber is a biological filter with Japanese filter mat, should the middle chamber also be a biological filter or should it be another prefilter with brushes. I seen both approaches described in articles and catalogs but have never seen any discussion of the advantages and disadvantages.

A. The problem with this type of question is that if you ask four different "experts" you are likely to get four different answers.
For an 8,000 gallon pond I would like to see two banks of vortexes each with four chambers, although you could possibly get away with the three. I always think that bigger is better as far as filters are concerned. It all depends on how many fish you eventually have in the pond, but most of us grossly overstock the pond especially after a few years when the fish really start growing.
Except for the first vortex settlement chamber all the others should have Japanese matting.
I put your query about vortex size to Peter Waddington of Infiltration, and here is his reply:-
My recommendations for a 6,000 gallon pond with two bottom drains:- 2 banks of 3 units (prime vortex plus 2 bio) 40" dia. x 50" tall. For 8,000 system add one more bio to each bank.
Bio units all Japanese mat cartridges heavily aerated. Unquote.
The maximum flow rate is usually determined by the size of the pipework from the bottom drain, and between the chambers. For 4" (110mm) pipework is usually said to be 2,400 gallons. The supplier, or manufacturer, of your vortex chambers should be able to discuss the pumping rate in connection with your particular installation. If they will not do this then I would look to another supplier.

Q. Vortex chamber - is this a recent trend?A friend of mine works for Sulzer who make pumps,pipes etc for oil rigs and he said they use this system for separating oil from sand/water mixture on oil rigs! I wonder if that is where it was gleaned?

A. Vortex chambers were first introduced into UK koi keeping in the late 80's by Peter Waddingtom of Infiltration Ltd. The main idea was to enable the koi keeper to remove the solids, such as fish waste and leaves, from the system before they entered the filter system and so reduce the workload on the filters. This started the present trend of taking the water from the pond with bottom drains instead of the previous recommended idea of mid water. This is accepted practice now for many serious koi ponds. The bottom of the vortex can be drained out 2 or 3 times a day with a minimum loss of water, and this is considered important in the days when water meters may have to be fitted. Pulling bottom drains once or twice a day can lose a lot of water. A vortex chamber definitely does remove the larger heavier waste, but will not deal with small floating debris such as small strands of blanket weed or smaller lighter particles. To keep them from entering the main filter the first bay usually has brushes or some easily removable media such as Flocor. The Vortex chamber has been around for many years where it is necessary to separate two substances. It in fact works as an inefficient centrifuge.

Q. Why is a Vortex chamber any better than using two filter chambers?

A.The idea of using a vortex chamber is to remove as many of the solids as possible before the water enters the filter system. This removal of the solids is important to prevent the build up of mulm etc in the first bay especially if the water is drawn from the bottom drains. If the vortex chamber is working correctly then you can see the waste dropping to the bottom of the chamber and then this can be removed two or three times a day with the minimum loss of pond water. The vortex chamber will not remove small floating debris that is suspended in the water and this will travel over into the first chamber.
If you do not wish to use a vortex chamber then it is possible to have an extra bay before the filter system which will act as a settlement chamber. In this case you need to have baffles and/or filter brushes to trap the solids. These brushes will then need more time spent on cleaning them than the regular release of solids from a vortex chamber, and is the main reason most of our members choose to use a vortex chamber when building or updating their ponds.

Q. You have convinced me to use bottom drains feeding a vortex chamber,although a well known book recommends not to disturb the bottom water in winter months, your thoughts on this would be appreciated.

A. The book you mention is excellent, but it was published in 1989, and at that time Vortex chambers were very rare and not generally accepted.
Asssuming your pond is not heated then it is adviseable to draw the water from midwater in the very cold months so as not to disturb the fish if they are lying on the bottom. The midwater pipe can be connected to the vortex chamber, but then the chamber will only act as a normal settling chamber as it cannot remove light floating debris only the heavier waste. If you do this then it is adviseable to have a means of flushing out the bottom drains occasionly as waste and debris will accumalate there.
A page on Mid-water pipework has now been added to the construction pages.

Q. Supposing I have 2 drains and a mid water how do these physically connect to a vortex? The pics I've seen only look to have 2 entry points to the vortex.

A. Vortex chambers are usually built to order and you can specify one, two, or three entries. The more entries you have then the more disturbance there is likely to be in the chamber. I would recommend connecting each bottom drain to it's own entry and then connecting the mid water feed with a tee piece into one of the bottom drain pipes just before it enters the vortex chamber. It will come after the 4" valve from the bottom drain, and will also require a 4" valve so it can be isolated. You then use one or the other, and of course shut off the other bottom drain when using the mid water feed.

Q.I have been offered a "deal" on replacing my (round) vortexes for square topped ones.I didn't take it as far as money because I think that things are getting back to where they started i.e. areas of dead water-what do you think?

A.I was looking at these at KOI'97 and had a talk with the fellow on the stand. On the strength of this one of our members is going to use them on his new pond. The theory appears to be that the water enters into the vortex section and this forces the water around the outside edge and so it is then able to flow up through the square section. The advantage of the square section is that you can have a larger volume of matting.

Q. With a 15 x 10 x 6ft deep pond I am proposing to have two bottom drains, feeding a large vortex.

A. OK. The vortex should be at least 3ft diameter and the part above the cone as deep as possible. See website for dimensions for one type of chamber.