Cleaning the mirror of your Meade LX90 LNT telescope will result in better light quality, a longer-lasting telescope, and overall better optics. Every once in a while, you need to care for your reflector telescope by cleaning the large mirror at the base of the telescope. This is a moderately complex process that will require some household tools to do, but no special chemicals.
Fill your 5 gallon tub with distilled water. Add about 5 drops of the dish soap into the tub, and slosh the mixture around to get some bubbles emerging out of the water.
Remove the 3 Phillips screws on the bottom of the LX90 telescope base, and gently tug on the base to remove the mirror cell.
Lower the mirror carefully into the distilled water tub, touching it only by its sides. Submerge the whole mirror; if some of the mirror is still exposed, add distilled water to the tub.
Slosh the water back and forth over the mirror for 10 to 20 minutes, or until the face of the mirror looks clean. If there is a stubborn piece of dirt on the mirror, drag a wet cotton ball across the dirty spot to remove it.
Lift the mirror out of the tub, and pour distilled water over the mirror until all of the soap is removed from the face of it.
Set the mirror on your towel, and let it air dry. Do not use anything to dry it off, or you could leave scratches on the surface of the mirror.
Don't move the mirror while cleaning it. This will result in poor optics when viewing through the telescope.