Mechanical filtration theory

[Last Triumph]

I'm now keeping discus so naturally I'm doing lots of reading. I keep reading the importance of having clean water from a mechanical perspective (chemical filtration being an obvious given).

This got me thinking about the logic behind this mindset.

Scenario A: Highly efficient suction collects all the solid waste from the tank and stores it in typically sponge filters where it accumulates and slowly breaks down to be dealt with by the chemical filtration.

Scenario B: Poor suction (slow flow rate) fails to efficiently remove the solid waste from the tank which then settles and collects on the substrate, eventually breaking down to be dealt with by the chemical filtration.

In both scenarios, the water circulating the tank is in contact with the same amount of solid waste, the only difference being where the solid waste is located - in the sponge or on the substrate.

The big difference is the aesthetics, but biologically, is there a difference from the fish perspective?

In old school fish keeping before canister filters when under gravel filters were used for decades, the solid waste was captured to degrade in the substrate, so why is it such a no-no now?

What I guess I'm asking is - is the fuss about super 'clean' water from a solid waste perspective a red herring? As from where my head is at currently, all high efficiency mechanical filtration does is move the solid waste from point A to point B, which then degrades in the same way, at the same speed, using the same biological process, surrounded by the same water the fish swim in.

Thoughts?

[fr499y]

A doesn’t get disturbed by fish, B does. Maybe that’s the logic behind it?

[plankton]

I'm not going to disagree on the theory. Some of the bigger aquariums still use undergravel filters for their huge tanks.....
The waste will also get used by plants.
I agree it's mainly aesthetics.
The only thing that may be slightly different is the rate of breakdown and if it's still in the tank there won't be as many "munchers" to break it down, and it's breaking down directly where fish are and it could pose a problem for bottom feeders.

[LookoutTrout]

There is a problem with slow flow rate that I found with an Aquaone filter.
The filter was designed with a bypass so if the media gets clogged water keeps flowing. The pipes it was supplied with were too narrow and quickly clogged slowing the flow rate right down, when the filter was used with the supplied fine sponge this meant that I'd go to clean the filter after a month and find the media still looked brand new because all the water flowed through the bypass route.
Without the fine filter it worked briefly but had to go as I was doing a full hose clean every other week.
So most filters probably need a decent flow rate to make sure water passes over the biological media.

[Last Triumph]

The reason behind my question is that I have a really nice Aquael 2000 Ultramax which has 6kg of Biohome in it and good sponge filtration, too. All works like a charm and water params are great.

The issue is that the flow rate is such that whilst good, in my tank a fair bit of the fish poo sits on the bottom of the fine sand substrate and doesn't get sucked up. Some does, but not all and there are no bottom feeders in there to keep it mobile and drifting to the filter inlet.

It appeared to conflict with the stance that discus need clean water to thrive, to which my logic mind raised the question - same water, same amount of waste, only difference is location where the waste breaks down.

[black ghost]

Clean water has nothing to do with where the muck goes. It’s not about getting the muck out of the tank, it’s about fine particles being in the water, which can irritate a fish’s gills as they pass the water through them.

Those filters that let the water bypass the media (ie not get filtered) are missing the point. You don’t want the water to be bypassing the media, ever.

When you refer to chemical filtration you mean biological filtration.

Mechanical filtration is about removing solids. To get it properly ‘clean’ you need enough of a turnover, wherever the poop goes, and if the media don’t trap it all you need finer media, eg fine wool, polishing pads etc.

It doesn’t matter where the poop is if it’s not up in the water.

[LookoutTrout]

I'd disagree with bypasses being a bad thing. If 25% of water going through a filter bypasses the media then it will go round again with a 75% chance of going through the media that time. It's ok as long as a decent amount guess through the media, so the filter needs to be well designed.
If there's no bypass then there's a chance the pump will overheat when the media gets blocked.

[mikeyw64]

maybe what you need to do is run 2 filters


One for polishing and scrubbing the water so it's aesthetically pleasing to you as the fishkeeper and one to ensure the water is healthy for the fish you are looking after

[black ghost]

I'd disagree with bypasses being a bad thing. If 25% of water going through a filter bypasses the media then it will go round again with a 75% chance of going through the media that time. It's ok as long as a decent amount guess through the media, so the filter needs to be well designed.
If there's no bypass then there's a chance the pump will overheat when the media gets blocked.

And if there’s not a decent amount going through the media? That’s my point. I’ve known plenty of them that get more and more blocked (they all do unless prevented) until not enough water is flowing through the media. Then the ammonia rises…
As for overheating, that would just be down to gross negligence.

[black ghost]

maybe what you need to do is run 2 filters


One for polishing and scrubbing the water so it's aesthetically pleasing to you as the fishkeeper and one to ensure the water is healthy for the fish you are looking after

You can do all that with one filter.