There could be any number of reasons for slow growth but it’s generally going to be obvious from looking at the foliage if it’s a nutrient issue and they are over or underfed, or have pH problems.
Usually slow growth IME is from some other environmental issue like watering issues or lighting or compacted medium or low temps, etc.
Usually slow growth IME is from some other environmental issue like watering issues or lighting or compacted medium or low temps, etc.