Weed is a demanding on nutes is all... you just need a big enough system to support it. That in itself is enough to justify not doing it imo... when things are well established tanks are easy af they look after themselves... that does not happen in a week or a month and most consider an established system probably closer to a year.A good friend here runs an Aquaponics farm. The setup is the difficult part. you have to balance the chemistry before adding any critters. I've worked with his system enough to know something about it. 90% of the things you just mentioned are all self-adjusting once the system is properly running. Aquaponics is really the Organic version of Hydro. I've spent at least 4 years looking at his system and discussing how to get the best results.
The reason I bring it up is because I keep hearing it does not work well for weed. That seems totally backwards to me because no matter what he planted, it sprouted and grew to maturity in record time. He never planted weed (that I know of) so that's my issue. There are more nutrients in his system than the plants can take advantage of. What makes weed so different?
Trust me when I say you are likely going to have issues for a month and maybe a few.
So he must do water changes if his plants don't keep up?