A couple additions to the above thoughts. It may not be over-fertilization leaving salt deposits in the pots' soil, but the use of chemical fertilizers doing it. Try using an organic fertilizer which contains no salts at all.
If chlorination is the problem, here's a simple tip: Fill your watering can and allow the water to sit severl hours - to 24 hours first, to allow the chlorine to evaporate first before using it to water plants.
