Actual filter media will be fine - just rinse with treated tap or tank water to remove debris, then store damp at cool room temperatures ... eg replace (rinsed) media into baskets, pour some treated tap water over, filling to a couple cm's in bottom of filter, then close over to maintain humidity - you want to maintain damp + oxygen/air, so don't seal air-tight.
When filter can be restarted, just return to tank as normal - there will be a delay of a few days as filter bacteria "wake up" but it's nothing like waiting for a tank to cycle from naught.
Do clean tubing etc, otherwise when you restart filter all that gunk will dump into tank.
For existing fish in tank, I'd go with daily water changes of ~50% IF this is what fish/you are accustomed to (if you normally do 25 - 30% weekly water changes, then change that volume - altums
can be very sensitive to change).
If possible add in a
Seachem Ammonia Alert - water change 25% (or more) if any ammonia is detected ... depending on bioload & feeding, you may need to do frequent water changes especially if fish are accustomed to only 25% water change (I'd do these morning & evening if needed)
While filter is offline, reduce feeding to smaller amounts & possibly alternate days BUT depending on altum size & tankmates, you may see "
hunting" so you'll need to adjust feed amount & schedule to suit these fish ... if your group of altums are not presently "
hunting", you don't want to trigger this behaviour.
I'd want to maintain plant growth as much as normal ie powerhead for circulation & usual CO2, fertilizers, lights etc - perhaps reduce lighting/CO2 etc by 20% or so, but active plant growth will help to maintain good water quality so I'm not sure why you want to alter that so drastically ... depends I suppose on how high you run CO2 levels & whether anyone is about to monitor fish.
Your "helpful" bacteria will be present on various surfaces in the tank, including plant leafs & wood & substrate etc, so I expect fish will be just fine
🙂
You don't mention running temperature of tank, you might reduce this by a couple/few degrees as that will increase dissolved oxygen levels present in water column.
As night, perhaps run an additional air pump or ensure good surface agitation (heavily planted tanks can consume significant oxygen during the "dark" cycle)