Q. I understand using a water meter to measure the total gallonage of the pond and filters but I have no idea how to measure how many gallons per hour will be passing through the system so that I can control it.

A3. Another, but expensive way to measure the flow is to use an inline flow meter.

This one is obtainable from Rainbow Koi and costs about £95 in 2005.

It must be installed in a horizontal 1.5 inch pipe.

These good quality 1.5 inch and 2 inch commercial flowmeters are made by Georg Fischer and are very accurate but cost about £230 for the smaller one. They must be installed vertically, and are 16 inches high. They can be purchased from The Koi Warehouse.

Occasions where it might be worthwhile fitting one of these flow meters is when you have a large pump to say backflush a 30 inch sand filter, but this is too large a capacity to feed say a Nexus 300, and/or The Answer. The solution is to bypass some of the flow in normal operation to say a waterfall or a deep water return. The problem then is that you do not know how much water is flowing through the Nexus unless you are able to monitor it through a flow meter, and this is when they are useful.