I'm not sure if this was already covered, but do not do this.Forgot to mention I also change all 3 filters once every 2 weeks.
Every time you do this, you are killing off all your beneficial bacteria and re-setting your whole cycle.
The only thing I use in all my filters is sponge and all I do with this, is give it a gentle swish and squeeze out in a bucket of old tank water.
If you have charcoal or any ammonia-removing products in your filter you might as well throw these in the bin and purchase either sponge or some kind of bio balls. This will give your beneficial bacteria maximum surface area to colonise.
It is a fallacy spouted by companies that you need to regularly change your filter media. They only want to sell more product.
If that was me, I would be finding the biggest filter possible and stuffing that tank full of fast-growing stem plants. If you have the right light and fertilise them regularly, the amount of ammonia they can utilise is astounding.
I had a small sorority (7 gallons and 5 females) that was never cycled, but that never had any ammonia readings as I had so heavily planted it, and did partial water changes every few days for the first month.
Definitely gravel vac regularly. With no live plants to utilise the waste that accumulates on the substrate, you are only going to be leeching ammonia out into the water column.
Fish should not die from vacuuming the substrate. In most tanks, it should be an essential part of weekly maintenance.
Also I highly recommend purchasing a liquid test kit for ammonia, nitrite and nitrates. Trying to cycle without test kits is like trying to do it blind. You cannot tell the quality of your water just by looking at it, and in fact, some of the most toxic water can appear crystal clear.
Good luck. It's great to see you care enough to seek advice.