I agree with tank.
However, over watering is more of a symptom than a cause.

Almost any problem slows growth and that slows transpiration.
If a plant that size stays wet for several days there is something wrong.
A healthy, well lit, plant will use water rapidly.
When it suddenly stops "drinking", it's time to find out why, yah?

Suggest that you obtain a 100x variable microscope.
They run about $10 at da shack.

Examine the apical meristem, (growing tip), thoroughly.
Snip off a lower fan leaf and examine the underside, near the veins.
The borg are easy to find.
So are most root aphids.
But the most recent crop killer has been Broad mites.

Early symptoms are leaf clawing and low transpiration.
They can only be seen under high magnification and even then, it's not easy.
If you find mites, examine the eggs.
BM eggs are "bumpy" they have many, well defines, knobs on their surface.

There are a lot of different kinds of mites.
Some helpful, some nasty.
Broad mites are the worst kind of nasty, IMO.

Let us know what you find and we'll be happy to offer solutions.

Aloha,
Weezard