Sump with only sponge?

[Toby_H]

Bacteria will grow on almost any/every surface in the system. So we should expect an extremely thin layer of them over virtually everything.

With the exception of breeders who overstock bare tanks with no substrate for growouts, I doubt any of us have ever had a tank that had insufficient surface area to house enough bacteria for a proper nitrogen cycle even if we removed all of our "bio media".

Sponge only filters certainly will work. And as the filter clogs in one area, wherever the water continues flowing will just get more bacteria in that area.

 

[thiswasgone]

Clogging… bacteria can produce an extracellular matrix which helps them survive and can clog, e.g., a sponge. But there are limitations — energy. The amount of energy left in uneaten food and faeces is limited. After months of growth, the population reaches a point where there is no energy to support further growth, only to sustain the colony alive. The only limitation is available surface area. If there is plenty of it, the medium is covered with a thin layer of biofilm, which is effective in nitrification and oxidation of dissolved organic carbon (wastes in the water). No clogging occurs at this stage. The bacteria can even digest their own matrix to obtain energy. The bacteria/protozoa are starving and readily clean the water. This results in the best water quality. There are some limitations — the entry surface, where plant debris and faeces are prone to clog the surface. There should be a balance between the entrance area and the amount of waste… but apart from that, everything comes down to the overall surface area of the media. If the overall surface of the media is too low, the growth of the matrix makes the biofilm thick and restricts the flow. If there is enough surface area, no cleaning is necessary! The filter is self-cleaning.

I had a 45 ppi sponge that clogged after a year, but only when my little son overfed the fish. About 800 cm² of entry surface for 4 grams of dried food per day. I guess the dose was doubled during the overfeeding period. I had static K1 before for 3 years — no maintenance at all — I just wanted to change something… now there are sponges.

To sum up… filtration is easy: enough overall surface area, enough entry surface, and the filter is maintenance-free. You can calculate it with this tool… check:
https://www.monsterfishkeepers.com/forums/threads/feeding-and-filtration-planner.765567/

You're 100% right in terms of the typical home/hobbyist aquarium which is also why I stated in my last paragraph everything is going to depend on how engaged the OP wants to be with his filter. Most fish keepers won't house enough fishes (small or large) to actually have to worry about min-maxing nitrification so they can maintain a good enough bio-filter with most high-surface area bio-media. Of course this might matter if space is a large constraint but overall you can just throw in some sponges and pass enough flow through them to get a 2-in-1 filter; no real need to have a polishing pad in a well establish tank with weekly water changes. I did this with a heavily stocked 180 I ran a long time ago, used a 55g tank as a sump and ran it with only ~1ft^3 worth of plastic pot scrubbers I got at dollar tree.

As long as you're not over-feeding or over-stocking it's fairly difficult to cause major issues with your bio-filter.

 

[thiswasgone]

So...you don't need to ask yourself a "plethora of other questions" before building a filter...unless you just want to. No need to lose sleep because your filter isn't 99.9% "efficient". Virtually all of us have a vast excess of surface area for bacterial growth in all of our tank/filter systems right now. That is, by definition, good enough. Zero ammonia is zero ammonia, period. More filtration, or more efficient filtration, isn't better than "good enough". Your water won't be better; ammonia readings won't go below zero ; fish won't be healthier.

Haha exactly.

Bio-filter media selection is pretty pointless for most home/hobbyist aquarium since most people severely over-estimate how much media they need at all. Unless someone is overfeeding and/or overstocking most setups will work so long as you properly cycle your tank & filter. Just keep a consistent water change schedule to maintain 0ppm for nitrates. You'll drive yourself crazy over what type of sump design to use as it will lead you down a path of endless potential optimizations.

 

[triamond]

In 2005, I had a planted tank and was testing various sources of nitrogen for plants. I was removing the media from the sump until there was none left. Then I reduced the flow through the sump. Ammonium sulfate was added by a peristaltic pump at a dose intended to achieve a target of 5 ppm NH3 in the water.

However, there was no detectable ammonium in the water — everything was readily converted into nitrates. I stopped the experiment when fish deaths started. Without media in the filter, the water became dull.

Agreed, the uncleaned internal surfaces of the aquarium and sump should be enough to provide surface area for nitrifying bacteria.
But nitrification is only a tiny fraction of what is going on in the filter. There should be 20–100× more surface area for all the life in the filter, so it is not surface-limited.

 

[David R]

duanes our native shrimp don't tolerate the warmer temperatures of tropical tanks unfortunately, many have tried before and it just doesn't work out. I've never thought of growing our local mangroves in pure fresh water though, but it is something I'd like to have a crack at now that you've mentioned it! I've never seen them growing anywhere other than intertidal zones where the water is pure salt or very brackish, but the pods are everywhere at this time of year so it's worth trying I guess. Could be cool for an outdoor pond if it works!

jjohnwm that was a good breakdown of that epic post from T thiswasgone , thanks for taking the words right out of my mouth, and thanks thiswasgone for crunching the numbers in such detail! Jjohn its interesting to hear you've actually experimented with how much media you can move before crashing the tank, I've often removed roughly 1/4-1/3 of the bio media from a canister on one tank to kick-start my quarantine tank for new arrivals with zero impact on the main display, which has made me wonder just how much more could I remove. Some seeded media from the main tank and a bit of driftwood equals instant cycle for the new tank. I can't even remember the last time I've cycled a tank from scratch (probably not this century anyway).

I think you (and others who have also suggested it) are right that almost all aquariums have vastly more bio media than is required on paper, but I guess that's better than not having enough. I'm still toying with the idea of the HMF sump but will definitely try incorporate some sort of planted refugium type chamber, A; to provide opportunity to keep a wider range of fish, and B; provide some additional filtration.

 

[phreeflow]

It seems everyone is saying the same thing in different ways and it’s what makes this forum so much more valuable and interesting than short-from social media. I appreciate the different approaches as it gives a fuller understanding.

So basically…the consensus is you can use whatever you want in the sump and it’ll work but for ease of maintenance, those sponges seem pretty compelling. In fact, I’m convinced enough to throw out a bunch of bags of nasty ceramic media and place an big order of sponges for my own setup. Thx all

 

[thiswasgone]

Agreed, the uncleaned internal surfaces of the aquarium and sump should be enough to provide surface area for nitrifying bacteria.
But nitrification is only a tiny fraction of what is going on in the filter. There should be 20–100× more surface area for all the life in the filter, so it is not surface-limited.

Yup, heterotrophic microorganisms do a large amount of heavy lifting and require much more surface area compared to the autotrophic bacteria but i've already put in a large math post in the thread; don't want to go too overboard and potentially off-topic to talk about microbiology haha.