The only way to be certain which nutrients your citrus trees need is to do a nutrient analysis. Most home gardeners use a soil test, although leaf tissue analysis is possible (but more expensive). Most Florida soils are low in nitrogen, phosphorus, and many micronutrients. Use a fertilizer based on your soil test results. Typically it's safest to fertilze citrus trees several times per year from late winter through late summer. Avoid fertilizing in fall.
If your water is high in salts, you may need to leach the salt content by flushing the soil with distilled or rain water.