I have several years of exp with coir as soilless media.
Item #1
SODIUM
Rinse your coir until the water runs clear.
Add ph adjusted nutrient solution. (NPK including cal and mag)
Rinse again. Minimum volume of water is 3X coir IMHO
Processing of coconuts generally involves soaking in sea water to loosen the fibrous exterior.
During this time large amounts of salt are absorbed.
I have personally measured rinse water from fresh coir with a TDS of 1000ppm.
Item #2
Coir is deficient in calcium and magnesium. Your plants will be too if you fail to address this issue.
Watch for intervienal chlorosis as a sign of mag def.
Foliar feed epsom salt @1tbs/gal to correct.
It can be supplemented into soluble fert solution @1/4tsp/gal as part of regular feeding regiment.
Another way (and how I finally slayed this beast) is DOLOMITIC LIME
This is commonly called "Ag Lime" and is crushed limestone containing both calcium carbonate and magnesium carbonate.
1tbs/gal in your potting mix, it is slow to dissolve and has a ph close to 7 so there are no swings (wood ash anyone?
)
These are two major issues/drawbacks concerning the use of coir.
Once you address these coir will become like a miracle media.
My recipe
5 gallon bucket
drill a pencil sized hole 3 inches up the side NONE BELOW THIS !!!
rinse coir
mix your coir with 25% perlite and a handful of dolomite
plant your nanner
water with soluble complete ferts @500ppm UNTIL WATER COMES OUT OF THE HOLE
to check water needs simply lift (I kick) the bucket to feel the weight heavy=ok light=add water till it comes out of the hole
hang on to your britches
if you grow tired of your (giant freakin) nanners going all Mary Poppins every time a breeze blows then you can bury the bucket half way in the dirt
it will still drain, although more slowly
If 5gals is too small, then consider a 18 gal or larger rough tote or the like.
Just be aware that coir has huge absorbency and a small plant like 1ft WILL be waterlogged in a container this size. A strong 3ft plant is the smallest I would put in a 18 gal tote.
In a 25 gal I would expect a 15ft+ plant to do fine, maybe only needing watered every other day. The more perlite you add the less water holding capacity.
coir is fantastic once you understand it