Gee jack, there are a number of things that may be effecting your
First, spider mites alone, if severe enough, can impact and even stunt
the growth of plants. It may be that the infestation may have been well
established before you ever acquired the plant.
Secondly, palms ar susceptible to fungal attack, but is general a
combination of poor growing conditions in combination with overhead
Third, the condition called chlorosis, is the sickly pale yellowing of
the leaves. It is due to the lack of available iron for the plants
uptake, whether it be due to poor soil conditions, or high pH, alkaline
conditions of the soil preventing the plant from utilizing the iron.
Good aeration of the soil is needed to allow for iron uptake by the
plant. Either with new soil, or an iron additive, after the plant has
been given a healthy drink, it is necessary that the soil be allowed to
dry slightly to ensure the iron is absorbed sufficiently.
And fourthly, the fishtail palm has a striking appearance, known for
both its uniquely shaped leaves, as well as for it's size, this plant
can easily reach heights of 6 feet or more, so understandingly, frequent
furtilization is discouraged.
I hope this helps, jack