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We've talked about mechanical filtration, a bit on chemical filtration, and biological filtration. We've had little side topics about water modification and a bit on plants acting as nitrogen filters (even though I said I would not - I lied, but I was referring to plants as the sole filtration technique then). So what do we have to do to implement all of this ideal theorizing into the real world of the aquarium, and consider what is required to keep it operating at the optimum levels.

Tank Sizes

First there is going to be another digression - did anybody ever accuse me of digressing before? We need to think about flow rates and turnovers per hour. Your 20-gallon tank does not hold 20 gallons of water. Tank sizes are manufacturer shorthand. They have little to do with reality under the best of circumstances. The manufacturer takes the (rounded off) exterior dimensions of the tank: For Perfecto's nominal 20H (20 gallon high tank), 24 ¼" x 16 ½" x 12 ¼" this rounds off to 24 x 16 x 12. Multiply those dimensions together to get 4608 cubic inches total volume of space occupied by the outside dimensions of the tank. There are 231 cubic inches in a US gallon (versus 277.42 in an Imperial gallon), so 4608/231 = ~19.95 US gallons total volume occupied by the tank. This is remarkably close to 20 gallons, so we can grant this as adequate shorthand. But that includes the plastic trim, the glass walls, and does not adjust for the fact that our tanks are not filled to the top brim, or that the bottom glass is above the base of the "outside" of the tank. If you want a better theoretical capacity, measure the inside dimensions of the tank to a bit below the interior lip of the rim. Both these capacities totally ignore the water displaced by substrate, rocks, other decorations, as well as the water volume which may be added to the total by W/D sumps, external canisters, FBF, HOB/HOT, etc. My most recent 55 reset measured out to 41 gallons actual water capacity without external filters, a recent 29 at ~23 gallons (both have substantial substrate volumes). So we have a very crude label with poor relation to reality, but it is handy shorthand.

One warning on over-generalizing, as we tend to do on the forums - different format filters do not necessarily directly compare in capacity or in needed turnover rates. Efficiency and effective particle size capture for mechanical filtration play very significant roles in those requirements. High efficiency units may not need as many turnovers to capture the majority of a certain size particle, or to expose most of the tank water directly to the biofilter. Less efficient units conversely may need more turnovers to do the same job in the same time. That is really no positive or negative judgment on either format of such units. It is just the nature of their design and engineering. Select the format that is friendly to you or to the particular setup, not necessarily the engineering behind its format. Do not attempt to compare different filter formats simply by turnover rates.

What Size Filter?

This is about filtration, so what does this mean on filter capacity required, and that great mythical measure of turnover per hour? Manufacturers, in their efforts to present the rosiest possible image of their products, frequently tell you what the output of a given filter "should" be. The output is measured in their test lab, using brand new equipment, no filter packing (repeat, no media in the filter - if the filter box itself is even used versus the drive unit only), and zero head (water return at exactly the same level as the tank water surface, but without meeting the resistance of standing water). So they give you a figure of say 100 gallons an hour. Great! That's five turnovers per hour in our 20H. TLAR (That Looks About Right), right? Hey, we have less water in the tank than the nominal volume anyway - maybe as much as 15-25% less, so our turnover is better still, right? Fergidit. We also have media in the filter (greater resistance to flow, lower flow). We have complicated our in-tank circulation by plants, rocks, ceramic castles, and a sunken galleon; so we don't have ideal mixing to say the least. In effect we have no idea what a realistic turnover of all of the water is in our tank. But the ever-kind manufacturer has given us a hint, something on the order of "Good for tanks of 15 to 30 US gallons capacity". These figures are the best to use in reality, with just a bit of translation. The 30 gallon tank estimate means something like " IF you have a heavily planted tank, with plenum, and total fish stock of 2 otos and one flagfish (female), plus 3 Amano shrimp". IMHO, the 15-gallon is the more realistic suggestion for the average hobbyist. There are some companies that actually do give pretty realistic suggestions, but even there, think about what you are putting in the tank - goldfish or most cichlids? Go to as much as double the estimated requirement (1/2 the tank size suggestion). Normal, which is to say overcrowded, tropical community tank? Use the small end of the tank sizes suggested for that filter. Is it a species tank of small Tetras in a school plus a couple of Otocinclus, with well under 1" per gallon adult size of the fish stock? Well, middle of the suggested range is pretty close. A bit of oversizing in filter capacity is cheap insurance. As the media builds up debris, both flow rate (i.e., turnover) and oxygenation of the biofilter bacterial bed decrease. The manufacturer should have considered this real world situation, but are you going to bet your fish that they did? Over filtration is not in itself harmful, so long as you do not have excess current in the tank for the type of fish being kept. So long as you do not allow that over-capacity to lull you into ignoring the needed cleaning interval on the filter media, you will be doing no harm. Reserve capacity, either biological or mechanical, is conservative. For better or worse, I am basically a very conservative tank-keeper. Some of my techniques may seem off the beaten path, but they are things that I have tested at length for my own use and my style of tank maintenance before I ever mention them on the boards, or suggest others might try them.

Filter Placement on/in the Tank

For most hang-on filters (HOT/HOB), choice is pretty limited on a standard tank. Do you like back right or back left? With some setups you might be able to use the end of the tank, depending on the tank cover and the room furniture arrangement. Despite all my neuroses about filtration, to me the most important item on the filter placement list is ease of access for me to do maintenance. Obviously, out in the living areas of the house, I want as much "mechanism" as possible concealed, but if the choice is between ease of access and concealment, access wins every time. Many folks reading this are already aware that silent operation is a strong selling point for me. That is one of the main reasons I use canisters, and the primary reason for my particular choice of brands. External canisters by the nature of using hoses and valves offer great flexibility in intake and return placement. You can pick up the water wherever you chose, and have it return to the tank wherever you want it. You can have the return above the surface, maximizing gas exchange, or minimize cover glass spray and surface disturbance by returning the water below the surface. If you are using spray-bar returns, these can be customized to maximize or minimize pressure per outlet opening by varying the size of the openings, or by increasing or decreasing the number of openings. These return spray-bars have traditionally been placed horizontally along the back of the tank. But they can be placed vertically in any tank corner, or horizontally along any glass wall, aimed wherever you want them to be. In general, smaller openings and maximum open space in front of the spray-bar will maximize overall current. Larger openings and minimum open space in front of the openings provides gentler, less distinct current in the tank. If you are a canister user, playing with a drill and a few feet of spare tubing can open a new world of current control for you. Intakes and returns may even be split, for pickup or return to more than one location.

Mechanical filtration placement if separate from biological is not very fixed for me. The small internals I use for mechanical filtration are subject to re-arrangement at any time. If I notice that debris is building up in some particular place in the tank, I'm comfortable moving the biofilter return and/or the mechanical supplements to try redirection of the water flow. The redirection is an attempt to get more of the debris into the mechanicals where it is easily and routinely removed. If that isn't practical, I'll just make a mental note to vacuum that area each water change.

Filter Maintenance

Since I do use external canisters, and tend to keep those for biofiltration only, I need easy access to the sponge prefilters I use to protect the biofilter itself. Much less access is needed to the canister itself as they are much less often cleaned. My supplemental mechanical filters tend to be internal canisters. These are not aesthetic masterpieces, but I can live with them, and they do need frequent access as well. Mechanical filters I try to clean at least weekly, by tap water rinses. How often you rinse your biomedia depends on your own particular setup- that will depend on your observation. The conservative approach is to use tank water for rinsing the biomedia, and I usually do this. I confess I'm a little doubtful of the need for preconditioned water here - exposure time is a big variable, but I'm not going to argue the issue. As I do tend to have redundant filtration systems, it might be less an issue for me than it may be in a single-filtration-unit tank. But as stated earlier and often, using tank water for this rinse is conservative.

How often do you really need to clean your filters? Only you can make that call, no two tanks will be the same. You can test flow rates from your filters, and change when you have lost one-quarter to one-third of the initial (clean) flow. I most often judge by eye. When I'm rinsing a mechanical filtration sponge in a catch bucket under the tap, if I have to rinse more than twice before the rinse water is largely clear, three times for completely clear, I suspect that I need to rinse more often. Or I need more (additional or larger) mechanical filtration. If you are keeping large messy fish (say perhaps Oscars, or adult sailfin plecos) it may be difficult to meet that standard. For such setups I would tend to select W/D filters with easy access prefilter sponges in the overflows. Those can be pulled and rinsed every day or every other day with less hassle than most prefilters.

Any water pump needs some upkeep. Impellers need gentle brushing periodically to maintain their flow rates. Their interior housing needs similar attention. Intake and return tubes may need cleaning periodically as well. Specialized brushes are available from the LFS or by mail order to assist with this. The first time or two it is done, it will seem awful and near impossible to you. There is a short, fast learning curve on this. It really is not that difficult after you have done it more than once or twice.

Filter Media Replacement

This is tricky. My best advice is to start out with the manufacturer's suggested media, replacements for mechanical media being done per their advice. If their advice is expensive and seems wasteful, try some repeated use materials. Biofiltration media should be handled conservatively, replacements being rare and careful. Once the tank is stable, don't be afraid to try other media and other types of media. One of my "things" is using largely indefinite-use media (sponges, ceramic noodles, plastic biomedia) with absolute minimum use-and-discard elements. Your choices may be different, and that is perfectly fine, just as is your choice of the filters themselves. You have to find out what suits your own style of tank care, and is comfortable for you. So start per the instructions, and once you have seen how that operates for you, experiment.

Water Monitoring

Water changes themselves assist in water quality maintenance, but are outside the scope of this article and will get just the minimum once-over-lightly review. For more detail see: Water Changes, Why, How Much, and How Often? Monitoring nitrate balance in the tank, along with GH/KH comparisons to your tap water can help you set a change schedule to complement your filter-cleaning schedule. If your nitrate is climbing faster than you like, you may need to increase the amount and/or the maintenance of your mechanical filtration - to get waste out of the tank before it is broken down. If your GH is climbing in relation to your tap or other source water, even if your nitrate is fine, you need to do periodic larger-scale partials or more frequent small-scale partials to reduce the buildup of minerals in your water from routine tap water replacement for evaporation. If your KH is dropping (pH likely will be doing the same), the acid production that is part of nitrification is overwhelming your buffering and you need more frequent or larger partials to maintain more even water quality for your fish. As a tank matures (over three months after full stocking minimum, more likely over six months IME), it does become more stable. But don't forget that the fish (unless full adult when added) have continued to grow, maturing also. This means there is an increasing bioload to be dealt with, so maintenance must keep up with the changes, even though they are slow. Larger, more mature fish mean more total nitrate and other wastes than when the tank was started 6 to 12 or 18+ months ago.

An established tank should not have any disturbance to the basic nitrification process (ammonia to nitrite to nitrate). The highly toxic metabolites (ammonia and nitrites) should not require routine testing. But, if things appear to be "off" subjectively to you, test nitrification (all three phases - ammonia, nitrite, nitrate) and pH and GH/KH. Those basic six tests of water parameters and how they compare to your tap water can tell you a lot about the status of the tank, its inhabitants, and how well your maintenance is doing what you think that it is doing. Along with this, be very skeptical of medicating display tanks. Any such extreme handling (my opinion) calls for routine nitrification testing during the course of treatment and for some days afterward. Manufacturers and LFS have been known to lie (intentionally or not) about the effects of agents on nitrification.

Summary

There is nothing magic about tank filtration. There are multiple types and brands with dozens of equipment sizes and configurations, which can be used to help you maintain your tank as well as you wish, with substantial variation in the actual filtration media used in each type. None is in and of itself right or wrong. Any equipment or technique can be used or misused. The trick is selecting the filter types that will do the cleaning job you want and need, and that will be easy for you to maintain. That issue may take several questions on the discussion boards to gather the information wanted for a particular tank setup. Even after that, the arrangement that suits me perfectly may well be a nightmare to you. That question only your personal experience can answer, but for starting and developing that idea there are a lot of us on the discussion boards here and elsewhere who will be happy to contribute our two cents worth with our own experiences. From those you may pick and choose ideas that have appeal to you and suit your needs and personal style or habits. Then you try them out for personal fit. Don't be afraid to admit (to yourself at least) that a particular unit was wrong, if not in and of itself by nature, then at least for your habits and usage. Advance planning helps a lot, but only personal usage and evaluation gives a final answer for your own use. If a unit is wrong for you, try not to think that it is wrong by nature if the problem is one of personal needs and habits (I cannot deal with equipment noise, my wife considers it "white noise" and does not mind at all). That is the hardest judgement call. The rest is just practice until you have it as comfortable as possible for yourself and your fish.

This series originally appeared elsewhere, and has been heavily edited and rewritten for use on this site.

Robert T. Ricketts, a.k.a. RTR

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