This is my current fluval 405 setup, I plan to supplement it with another filter, perhaps a 305 in the near future as I am at the limit for the 405 (100 gallon tall tank) but I prefer over filtering to help grab more detritus etc, unfortunately due to my hood design, I can not supplement with a HOB setup..
Turfed the stock carbon bags as they are good for removing odour and meds from the water, unless you have a NEED for carbon, don't run it, it is exhaustible, and requires regular replacement.
I bought a 2L tub of seachem matrix and i am running that i nthe 2 lower baskets, I filled them up and the remainder I poured over the stock biomax that comes with it in the third basket. My top basket has filter wool (shop didn't have polishing pads in stock) and I put this in the top basket purely for ease of access, this way it still polishes the water to high clarity, and when I need to change it I am not disturbing the remainder of the media by removing all the baskets to get to the pads at the bottom of the stack.
For a while, I was running another THIN filter pad in front and behind the stock fluval foam pads, there is room in there without affecting flow, but when they exhausted I removed them, waiting replacement stock. The "pre filter" thin pads I speak off didn't have a brand name attached, but it was a white "brilo pad" feeling pad, kinda scratchy, and similar to the chemical filter pads you can buy, only about 5mm thick at most, and you can cut a layer to shape to fit othe left and right side of the mech filter pads, this allowed me to have more bio filtration without sacrificing a basket for the pre filter mech media...
If I need to run carbon or some such, I take out the top filter floss and replace with carbon, or purigen or other such media, and again, it is in the top basket, so no need to disturb my biomedia. I have run phosguard in the top basket for a while to lower my phosphates, nice and easy..
In this setup, I can have clear water in a 100 gallon tall tank. There's 2L of matrix in there aswell as the stock biomax, all in all that is more than double what seachem state is required to handle 100 gallons, I also sent off an email to seachem asking their advice of running twice as much media as necessary ( according to their specs ) and they agreed it was a good idea.
I don't have an issue with the matrix clogging yet, only the filter floss does require changing thus far, and buying a bulk pack of filter wool is cheaper than buying fluval polishing pads, you just cut it to size and jam it in there..
1L of matrix should according to the company be ample for a 100 gallon tank, but IMHO you cannot have too much media. I will run a similar setup in my next supplemental filter, but I may change to eheim substrat to see how it is.. I don't really want to run one mech filter and one bio filter, I want to have the bioload evenly spread across the filters so that if one goes down or requires maintenance, the other is still doing it's job and keeping the fish happy, I work in the medical diagnostics industry, so I feel most comfortable with a backup system in place.. Mirrored backups that is..
Don't get me wrong, I am not pushing matrix, i think any quality media will do the trick, just stick with a proven product and you will be fine, matrix, eheim and biomax are all time tested products that work, steer clear of the noname media and you cant have a problem, but you can trial anything you like really.. I just won't experiment at the expense of fish health with unproven products. But for ease of this posts sake, i KNOW for a fact you can fit 2L of matrix in a 405 if you dispense with the carbon, but if you want to run carbon you can, you still have the "top" basket to play with.. A lot of posts recommend your mech filtration stages first, so sponge pads, then filter floss in the bottom basket and media in the top baskets, but i went with ease of access, and have no trouble with the matrix clogging, if I do, I will move the top filter floss basket to the bottom position and the problem is solved..
Hope this helps, let us know what you go with, i would be interested in other 405 setup options..
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