That would be 400 gal/week. This would cost a lot. Is there no
alternative? Perhaps filtering with charcoal?

- Francis

Even if carbon would work, it is far more pricey than a water change.

Not knowing where you're located, I'm betting that 400 gallons wouldn't
cost more than $2-3 bucks or less, and you water the garden with it, so it
isn't wasted. ~ jan

~Power to the Porg, Flow On!~