Algae formation in overhead tank
Every house has overhead tank. Majority of them are made of HDPE (plastic). A few are also made of RCC.
Most of those who have seen inside the overhead tanks (especially in summer) would have observed that the sides of the tank have a deposit of algae, which is characterized by its green colour.
What is the likely reason for this and whether this can be minimized, if not completely stopped?
A representative picture of the overhead tank is below:
- Representative overhead tank
- air vent in water tank.png (74.97 KiB) Viewed 22730 times
Some of the tanks may not have the tank air vent but necessarily have the air vent for outlet pipe. Very few may not also have the overflow pipe marked as 3.
You may notice that the air vent generally has a T fitted on top.
Growth of algae requires moisture and this is accelerated by the presence of light. Since overhead tanks are exposed to harsh sunlight, some light enters through the T openings of the vent pipes and also through the overflow pipe. The powerful sunlight partially gets reflected through these openings and the hot and moist environment aids the growth of algae.
To drastically reduce the chances of sunlight entry, I have slightly modified the vent pipe as below:
- Modified vent pipe
- Modified vent pipe.jpg (61.84 KiB) Viewed 22730 times
As you can see, to the T is added an elbow on both sides. This makes the outlet face down to the terrace and the chance of entry of sunlight is greatly reduced. This also makes it difficult for the feeble scattered light to enter the moist surface, greatly reducing the chances of algae formation. Please note that still algae might be present, but only in traces. I have confirmed this by making the change at my house.
Algae formation may also be witnessed even in underground sumps which have their lids open to direct sunlight. Also repeated opening of the lid with or without keeping it open for long can accelerate algae formation.
Compared to river water and bore well water, rainwater by itself resists the formation of algae due to its ORP (Oxidation Reduction Potential) being positive.