Fiberglass is commonly used to make hot tubs. This material can be easily scratched, but it is very durable when it comes to holding a lot of weight. When you own a hot tub, it is crucial that you drain the hot tub regularly in order to clean the interior of the tub to cut down on algae, grime and build up and also to keep the filters clean and working. Cleaning a fiberglass hot tub isn't all that hard, and if you drain it first, you don't need any fancy cleaning equipment or cleaners.
Drain the hot tub. This will get as much of the loose debris and dirt out of the tub as possible, which will make cleaning easier.
Take out and rinse the filter with clean water, or replace the filter if it is disposable.
Mix 1 cup of mild dish detergent with 2 gallons of warm water in the bucket and drop the sponge in. You want to use a non-abrasive sponge because abrasive surfaces can damage the fiberglass.
Wring out most of the liquid from the sponge and scrub the interior of the hot tub. Scrub the lights if you have them and get into the hard to reach places. This is where a lot of grime and dirt can hide and accumulate.
Rinse the interior with clean water (you can use a garden hose) and then drain the hot tub. Repeat until there are no soap bubbles left in the tub.
Scrub the exterior of the hot tub to eliminate dirt, dust, grime and film. Rinse with clean water.
Refill the hot tub and turn it on to heat up the water temperature. Replace the cover if desired.