Coarse Foam Pad

[F15FreeEagle]

As most or all of us know, there are a seemingly endless options of media to put in canister filters. And on top of that, there seems to be some debate on where to put the coarse pad that comes with most canisters. So a quick flash poll: do you put your coarse pad in the bottom, or do you put it somewhere else, after the water has hit the floss pads? Most canisters filter from the "bottom up" (all of mine do) so if you put the coarse pad on the bottom, this means that is the first thing the filtered water hits. Most manufacturers suggest putting it after some or all of the filter floss. However, I've seen several good arguments for putting it on the bottom. What say ye?

[Diana]

The water needs to pass through the coarsest media first. Then medium, then fine floss.
If you put the fine floss first it would trap all the debris, and clog up sooner.
By arranging the media in the correct layering each coarseness traps a different size range of debris. The coarse media removes the largest debris, but allows the smaller debris to pass through, to be trapped by the finer media.

I have seen what happens when this order is mixed up.
When there is a finer media ahead of a coarser media, the finer media does all the work, and does not allow coarse debris to pass through to the coarse media. The coarse media in such a set up ends up fairly clean, while the finer media gets clogged pretty soon.

There are other forms of media that may look like a coarse mechanical media, but is really intended as a home for beneficial microorganisms. This media can be used both ways. Used early in the set up it will trap coarse debris. This may coat the media so there may be low oxygen, so bacteria does not thrive. Used later in the system, after the debris has been removed, this media will stay cleaner and allow a really good population of microorganisms. I have seen this media sold for ponds or multi-tank filtration systems, where hundreds to thousands of gallons of water need to pass through. I am not sure if it is useful in a canister. Probably OK in a sump with a larger volume.

[F15FreeEagle]

I fully agree with this (this is how I have everything set up right now.)

But I am curious as to why the manufacturers instructions on mine. I have all Penn Plax canisters, and it says it filters from bottom up, Then it says to put the coarse pad on top? I don't get it.

I emailed their customer service about a week ago asking them for an explanation, but have not heard back from them.

[Diana]

Occasionally I will put a bit of mesh (fairly coarse) at the end of the line up. But only in this situation:
I reload my HOB filters to replicate the Aquaclear style: A basket with the media stacked. If I use fine floss last, at the top, it has fallen into the tank. By putting a stiff mesh across the opening this keeps the floss in place. Usually I will use a cut-off piece of the original cartridge; this is stiff enough to hold the media where it should be, and is made to fit in the slot of the HOB.
This mesh does nothing to filter the water, though. Well, maybe some microorganisms live on it.