It's a good idea to flush your medium out at least once during the flowering cycle. This gets rid of salt build up which will eventually bite you in the ass if you let it build up bad enough. Most of the time it isn't a problem but you'd be surprised. Just take them to the tub and run water into the pot until it starts running clear out of the bottom. Alot of garden gurus recommend flushing atleast once a week if you feed with every watering.