RewriteEngine on

RewriteCond %{REQUEST_URI} !^/jameswhitepools/poolchemicalsonline/./products\.php$
RewriteCond %{REQUEST_URI} !^/jameswhitepools/poolchemicalsonline/images/
RewriteRule ^([^/]+)/([^/]+)/?$ products.php?show=main&main_category=$1&sub_category=$2

RewriteCond %{REQUEST_URI} !^/jameswhitepools/poolchemicalsonline/products\.php$
RewriteCond %{REQUEST_URI} !^/jameswhitepools/poolchemicalsonline/images/
RewriteRule ^([^/]+)/?$ products.php?show=cats&main_category=$1 [L]