Going From 8 Litres Of Bio Media To 6 Litres...

[Abyss]

My Eheim 2080 has been dying a death in recent years. To be honest, I bought it used at a very good price so I'm happy I've had 5 years use out of it. Long story short, I need a new filter.
 
I keep a heavily stocked 400L Malawi Tank. I want to get the Fluval FX6 as I don't really want to go Eheim again (despite the good rep). It is also far more in my budget than a replacement 2080 (or similar Eheim).
 
My problem:
 
Eheim = 8L bio, 4L of Mech.
 
FX6 = 6L bio, + sponges.
 
So, I was originally planning to just put my bio from the 2080 into the FX6...but of course it won't fit. I'd be losing 2L of it...
 
...what impact is this likely to have? How should I go about this change? Should I use the mech (in bags) in place of the sponges in the FX6 too? Should I put some bio media where the sponges should go and remove gradually, changing for sponges? Should I run both filters for a while? (I was really hoping just to do a straight swap,)
 
Any advice appreciated. Thanks.

 

[eaglesaquarium]

It won't impact things much at all, honestly.  If you have an established colony (which is sounds like you do) bring over as much as you can, and the bacteria will just reproduce to meet the need.   It should only take a day or two before you have the bacteria to handle the load.  These bacteria can double every 24 hours (or perhaps even a little sooner) under the right conditions.
 
 
Trade out as much of the bio media as you can, and then test your ammonia and nitrite for the next few days.  If you see a tiny bump, don't be too concerned, and don't change the water.  The extra ammonia being present is what will cause them to want to reproduce to handle the load.  Just be careful how high it goes.
 
If the ammonia rises above ~0.005ppm of free ammonia change the water to lower it.  (use this calculator: http/www.hamzasreef.com/Contents/Calculators/FreeAmmonia.php  and input "0" for salinity)
 
If nitrite starts to rise, you can use salt to combat that.  (http/www.aces.edu/dept/fisheries/aquaculture/documents/BrownBlood.pdf)
Incidentally, 1ppm of chloride from sodium chloride (NaCl) is at a ratio of 1 teaspoon for every 100 gallons, and the chloride concentration needs to be 10X higher than the nitrite concentration.   It is best to treat the nitrite this way, rather than with water changes alone, as the excess nitrite present will also stimulate more bacterial growth.   Be careful using this method when dealing with salt sensitive species, and be sure to dissolve the salt in a container of water before adding it to the tank.

 

[TwoTankAmin]

Just a quick correction to what Eagle wrote- the NH3 red line level is at .05 ppm not .005 ppm. Anything under .02 ppm is considered safe for almost all aquatic life.
 
Also, you can find step by step directions for calculating how much salt is needed for any level pf nitrite in any size tank here http/www.fishforums.net/index.php?/topic/433778-rescuing-a-fish-in-cycle-gone-wild-part-il/
 

 

[eaglesaquarium]

 Thanks TTA, I was getting a little carried away with my 0's.

 

[Abyss]

Thanks guys, good info.
 
Think I'm going to go for it in the near future.