David

I am envisaging a pond in the tropics (day temp 80+F, night 60+) at a lodge. Since our guests have different attitudes to "swimming free" and also I am not confident about what critters might find the filter beds to be a wonderful home, I would like to separate the filter bed from the swimming area. That leads me to these questions:

1. What metrics are there for water exchange in a separated system? I understand that the filter area should be at least equal in surface area to the swimming area, but in a separated sytem there needs to be a flow from one to the other which is an important design consideration.

2. If there needs to be an organized flow from one part of the system to the other and back, is there an advantage in having aeration built into that (mini-waterfall or whatever) at either or both points of transfer?

3. Constantly moving shallow (warm) water from the filter area to the swimming area will create a temperature gradient in the swimming area. How can that be ameliorated?

4. How does anyone calculate water loss through evaporation and therefore the need to replenish the water in the system? There seems to be so many wariables (wind, humditity, temperature, rainfall, etc, etc....)

5. Any issues you are aware of in a tropical system vs a temperate system?

Thanks for any help you can give. I realize that the UK is not in the tropics (unless global warming has increased dramatically since my childhood...) but just thought I would throw these questions out there.

Robin

Hi Robin,

1) The entire volume of water should be circulated within 24 - 48 hours.

2) There is no disadvantage in introducing air. A waterfall is mainly for cosmetics but should not cause any problems.

3) Circulate the water in the swimming area vertically to disturb the water stratification (i.e. the cooler lower water churned up with the upper warmer water.)

4) There are calculation/approximation methods available, but even measuring all the parameters necessary (wind speed, vapour pressure, etc) is tricky and will only give you a snapshot of the evaporation rate. It is best to get information from a local pool supplier for the average water loss through evaporation.

5) I know of no issues myself. Natural Swimming Pools have been made in Australia and work fine. I found a paper on a Caribbean wild ponds and incredibly they contained no mosquitoes. Just like in Natural Swimming Pools, predators, like dragonfly larvae, control them.

And sadly, as far as this summer is concerned, the UK has has not warmed up that much since you've been away.