Soluble salts can play havoc with houseplants and may even cause death if the salts are not properly leached out.
Soluble salts are minerals dissolved in water.
Fertilizer dissolved in water turns into a soluble salt. After water evaporates from the soil the salts stay behind. As salts become more concentrated, plants find it harder and harder to take up water. If salts are allowed to build up to high levels, the plants take water out of their root tips, causing death. To combat this problem, be sure you water correctly.