What Exactly Makes A Tank "Over Filtered"

[Nemesis]

^ Ok, so do you think a lone fx5 would be able handle the bio alone on a 400, or would you need another filter for bio?

 

[tcarswell]

^ Ok, so do you think a lone fx5 would be able handle the bio alone on a 400, or would you need another filter for bio?

Id say if they filled the baskets with a decent bio media and cleaned the large sponges with tank water they could obtain proper biological filtration. But this all depends on the owner , the fish they keep , their water change schedule , what they feed. There is a million different factors. If it was my tank id have 2 fx5's personally. to help circulation and mechanical filtration I like my water not just stable but constantly clean

 

[MadBob]

spending money isn't important, moving water through media is.

if you don't mind building your own sumps in rubbermaid tubs and using media that doesn't have a churched up name you can set up very effective filters on the cheap.

Heavy duty rubbermaid tubs not the flimsy ones, the extra dollar and 8 cents goes a long way here.. full of crushed lava rock as opposed to microceramic biobeads that have magic bioforcefeilds to lock in good bacteria (find the rock in the landscaping department in any big box home improvement store, it's inert, more porous than most expensive biomedia, and literally costs less than dirt) with bags of carbon and sponge prefilters from your LFS will do the exact same thing as any canister filter on the market for a fraction of the price.. I assembled 2 15 gallon sumps like this for my new 125 for under 200 bucks.

 

[deeda]

I love the logic of this type of answer though it can be difficult for me to follow unless I read it a few times. I have added my comments in red.

An engineers take:

If you consider a volumetric flow, Q [m^3/s], and a flow area through the media, A [m^2], the filter with the lowest superficial flow velocity, Q/A [m/s] will yield the highest interaction time between the media and the fluid for the bacteria to do their job. This makes sense because it allows the bacteria in/on the media to utilize the nutrients easily.

Since the rate at which the compounds are converted should be independent of local concentration, there is no difference if the compounds are removed by a slow flow or high flow (higher local concentrations will exist at the onset of filtering with slower flow than higher flow if in both cases the media convert at the same rate). I'm not quite sure about this statement. It seems ambiguous & I would appreciate some clarification.

For a slower flow rate, and constant source from waste, the concentration will be higher in the slow fluid because it is being spread out over less fluid. However, a higher Q will yield better mechanical filtering yielding a "cleaner looking tank". Moreover, since the time scale of liquid movement due to filtering rate should be far higher than the concentration diffusion rate (dependent on the square of concentration which is already small before squaring) that the location of the sources should not matter, but again yields a cleaner tank and keeps the media from clogging.

Keeping the media from clogging is more important, since fouling will decrease the effective surface area, Again, I am assuming you are talking about the bio-media & if so, this is a very valuable point. Clogging the bio-media with fine particles & detritus will reduce the amount of surface available for the bacteria to reside in/on.

raising the superficial velocity, thus reducing the interaction time of the fluid with the media and require more "passes" of the fluid through the media to remove the same amount of compounds than a non-fouled media. Just a technical rant...

I think that an over filtered tank is one that has more filters, media, etc. than are needed for the fish you keep. This includes type, size, habitat requirement, how often they are fed, tank maintenance schedule, water circulation, live plants or not, etc. There are a lot of variables that must be considered.

A 75G tank with 10 young Mbuna being filtered by an Eheim 2217, with proper media setup, might be considered over filtered using the mfg. stated tank size of about 150G. But once those fish have matured, it may well be insufficient. Keeping an eye on the water parameters would tell you if you have enough filtration as well as the behavior of the fish.

Additional canister or HOB filters can be added to mitigate the increase in fish size or quantity but I think an important point that is often overlooked is filter maintenance. Just because you don't see the waste & debris in the tank, it is in the filter and is continuing to break down. Is there really a difference between having one model filter on a tank & cleaning it 1X month or having 2 (of the same model) filters & cleaning them 2X month? More frequent cleaning of your preferred filter may very well be sufficient.

I do agree with the previous comments regarding having more than 1 filter on a tank. For me, it is a fail safe if one filter should die or I break something during maintenance. All that said, I have added additional filters as my fish have grown & increased in quantity. I clean my filters on a regular schedule because it is the right thing to do. My fish seem happy, my water parameters are in check and my tanks look good.

 

[cchhcc]

Flow rate is the most over-emphasized. least important aspect of filtration efficacy. Media volume and dwell time are key.