The stick chlorine you use probably has a pH of under 3, and may be lowering the pH of the pool water. Low pH or low total alkalinity can result in corrosive water and staining of the pool's surfaces.
http://www.havuz.org/pool-problems/pool-staining.htm
If the chlorine level is consistently low you should check the level of conditioner (cyanuric acid) in the pool. Low conditioner levels results in the chlorine evaporating in sunlight. You could also consider regular dosing by hand rather than relying on the dissolving of the sticks when the filter is running.
If the conditioner is OK, the reason for the high chlorine demand should be investigated. I have been using the Pool Wizard for about 18 months and find I use hardly any chlorine nowadays. My pool is marcite and I used to have nightmares with algae every summer. I used to shock twice a week and still had some algae growth appearing. Now I almost never shock and add just a hanful of chlorine twice a week. What a pleasure!