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For conventional container culture, you can't depend on the grow medium meeting your plant's nutritional needs unless you're growing cacti or some plants in the succulent group. If you're watering correctly, that is if you're saturating the entire soil column and applying enough water that at least 20% of the water used exits the drain hole, you should be fertilizing about every 4th time you water during active growth, and maybe every 3rd time you water during the winter months. If you think about it, it makes much more sense to tie the frequency with which you fertilize to the number of times you have watered, as opposed to the calendar; this, because the intervals between waterings vary significantly throughout the growth cycle and most fertilizer is flushed out of the drain hole when you water. That is a GOOD thing. It ensures the TDS (total dissolved solids - salt level) in the soil solution remains low, and the ratio of nutrients, each to the others, doesn't become skewed to the point where an excess of nutrient A can cause the plant difficulty taking up one or more other nutrients. A perfect example occurs when container growers use "bloom booster" type fertilizers. The excessively high phosphorous levels in this type of fertilizer can cause a deficiency of calcium and/or potassium, and/or copper, and/or zinc, and especially iron; so, now you can see how important watering practices are.

If you're looking for a fertilizer recommendation, Foliage-Pro 9-3-6 is a full nutritional supplementation program from a single container. It has ALL nutrients essential to normal growth and it derives more than 2/3 of its nitrogen from nitrate sources and uses no urea (as a nitrogen source).

A pH of 6.0 is a bit high, but FP 9-3-6 is an acid-forming fertilizer and should help with that as long as the water you're using isn't too high in alkalinity. If after using it for a couple of weeks the interveinal chlorosis doesn't go away, you might need to acidify your irrigation water a bit with white vinegar - a bridge to cross when you get to it.

Al