N-HoneyGourami N-HoneyGourami
  • Just popping in
  • Just popping in
  • Joined: 5/10 13:36
  • Group: Registered Users
  • Posts: 9
  • Posted on: 11/10 13:16
Changing from Fluval U3 to U4 #1
How do I swap from a U3 to U4 filter?

Can I just transfer the media/sponges and add new bigger polymax? Or should I run both together with new media and sponges for a couple of months?

If I run both together how would I know when the U4 is cycled? Seems risky turning the U3 off as the bacteria will die quickly? It costs too much for me to keep both running long term (going to cycle a separate sponge filter in the main tank as a backup filter eventually).

So many questions 🤯

Has anyone done this before?

Current stock: 4 x honey gouramis and 4 x platys. 125 litre tank. Not getting anymore fish until this is sorted.

Thanks 🐠🙏
Fishlady Fishlady
  • Tropical Moderator
  • Tropical Moderator
  • Joined: 6/7/2010 19:26
  • From Worcestershire
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  • Posts: 13384
  • Posted on: 11/10 14:13
Re: Changing from Fluval U3 to U4 #2
Yes, you can transfer the media which will instantly cycle the new filter. This is by far the best way, as running side-by-side there's no guarantee that the new filter will ever cycle.