All my plant books say flowering plants should receive fertilizer high in phosphorus and low in nitrogen but many of my tropical plants like acidic soil and those fertilizers are mainly nitrogen. All my plant books say flowering plants should receive fertilizer high in phosphorus and low in nitrogen but many of my tropical plants like acidic soil and those fertilizers are mainly nitrogen. I find these plants are tougher than the books credit them. Most seem to tolerate a little variation from the preferred conditions. The relationship between phosphorous and nitrogen in the soil is the key to flowering.
Nitrogen moves through the soil fast than phosphorous.
The source of water is probably doing more to affect the pH than your fertilizer. Use rainwater, water from the dehumidifier or distilled water to help with soil acidity. Hello Linda, Blackspot causes the symptoms you described. Remove infected leaves as soon as they appear. Fall cleanup is also very important.