Consider the following statements regarding coagulant aids: 
1) They are employed when temperature is low as they then accelerate the process of coagulation. 
2) They are employed when flocs are small and water is coloured. 
3) With their use, water purification capacity of the plant is increased. 
4) Most widely used materials are oxidants, absorbents, weighing agents, activated carbon and polyelectrolytes. 
Which of the above statements are correct?