Converting our Swimming Pool to a Natural Pond with Edible Fish (1)

We had to drain half the water out of our pool to remove the excess salt

Converting our Swimming Pool to a Natural Pond with Edible Fish (1)

September 2014
In September we turned off our pool pump and noticed an immediate ~$200 a bill decrease in our electricity costs.

After a few days it took on an evil green hue. After a few more days we observed water beetles and mosquito larvae - lots of mosquito larvae - and deduced that the pool was ready to introduce fish. So we first went down to the local lake and caught (after much effort) about 17 minnows to keep the mosquito larvae at bay.

These turned out to be gambezis, which are a bit of a nuisance here, apparently. Not surprising, apparently, as according to Wikipaedia: Fertilization is internal; the male secretes milt into the genital aperture of the female through his gonopodium.^[3][9] Within 16 to 28 days after mating, the female gives birth to about 60 young.^[3][10] The males reach sexual maturity within 43 to 62 days. The females, if born early in the reproductive season, reach sexual maturity within 21 to 28 days; females born later in the season reach sexual maturity in six to seven months.^[1]

Apparently our females were born early in the reproductive season. By Christmas, we had about 3 million gambezis in our 55,000 litre swimming pool. They thrived. And, within a few short days, they had dealt with the 3 million or so mosquito larvae. One problem solved.

About the same time I bought some (expensive) aquatic plants. They promptly died. So we took some water to be tested and found we had about 6000 ppm salt. About twice the concentration that plants could tolerate. Hmmmm we should have done that first.

A few rains later, we took some more water down. No change in concentration. The gambezis loved the briney water, but the plants didn't. That's a problem for a natural pond, which relies on plants and fish being in some sort of balance.

That's when we drained the pool. The lawn didn't like it much: it died as well. Oh well.

About this point we got some advice and found we needed some gravel on the bottom of the pond. Our advisor thought it would be a good idea to take the depth out of the pool, and put enough blue metal in the bottom to make the entire pool about 1 metre in depth.

It took one trailer load of blue metal to realise that we needed to spend about $1,800 in blue metal to get the depth about right. Another plan bit the dust. We put about 4 inches of blue metal in both the deep and shallow end, and filled up the deep end with bricks and rocks to provide "hides" for fish and the marron we want to keep. It's ugly, but I reckon the plant life I am planning will hide the bottom from critical eyes. The pool took on a thick bluish sludgy hue, and I feared for the gambezi.

At this point we filled the pool back up with fresh water and let it settle. Once the rock dust had settled, the gambezi became visible. In the meantime they had doubled in numbers. These guys are hardy! No wonder they are considered a pest.