Reducing the hardness can ...

Reducing the hardness can reduce the scale, but there can be other scaling as well (e.g. based on Iron).

So my suggestion would be to get in contact with a water treatment company to analyze the used water quality. They then can suggest a proper treatment for both, the scaling and the biological hazards in your cooling tower. Please beware that e.g. changing the pH of your water can effect other parts of cooling system (like metal heat exchangers, where scaling or corrosion is unwanted, too). Therefore this has to be done with care.

If you cycle the water within the tower, another parameter, which may influence the scaling it the amount of effluent water you have compared to the evaporative water loss. If you increase the effluent, that may as well help.

Depending on the severeness of the scaling, after you chosen the right water treatment, you have to clean or exchange the fill inside the tower. Additionally to the biological problem, severe scaling can also cause structural and thermal issues within a cooling tower.