I have a planter of bamboo that was looking decidedly peaked. It did not
only look ragged and had die-back on leaves, but newer leaves were very pale
green, and often started to show signs of the tips dying back before the leaf
was even fully developed. BRBR

In my experience, bamboo actually does very poorly as a bonsai, especially
indoors. I don't bother with it any more. I doubt you have a fertilizer
problem. Check for spider mites. Repot it in a fast-draining soil and put it
outdoors as soon as possible.
Iris,
Central NY, Zone 5a, Sunset Zone 40
"If we see light at the end of the tunnel, It's the light of the oncoming
train."
Robert Lowell (1917-1977)