I suspect that the answer is in what you have said about having no rain for several weeks, and I suspect that during that period you have had a fair amount of sunshine and fairly warm days which can lead to an algal `bloom`, and the water turns cloudy, or even green when there isn`t a balance between the mineral content of the water and the quantity of plant life.
Quite simply, if you have enough plants growing in the pond they will take out sufficient of the minerals in the water to starve out the algae which cause the clouding. The best plants for this purpose are the submerged oxygenating plants which usually grow quickly, but any plant which has its roots in the water will help, and lilies are pretty demanding in this respect - their big leaves also help shade the water and thereby reduce the effect of the sunlight.
If your plants are all growing well (particularly the submerged ones) I would let well alone and let them carry on, and remember, the barley straw isn`t an overnight cure, it works, but it can take several weeks to work. You can buy chemical preparations which are supposed to clear green or cloudy water without causing any harm to plants or fish, but these often simply don`t work, and you shouldn`t need them once the pond settles.
