Note: Before you read this article, you should be familiar with the various types of filters and filter media available. If you need to brush up on this area, please read this article first.
When selecting filtration for an oscar tank, you will need to keep a few things in mind. First and foremost, you will need to remember that Oscars are very big and very messy creatures, probably messier than any other fish you have kept. They eat a lot, and a lot of what they eat ends up coming out of their gills in a mashed-up mess. The rest comes out the back end as prodigious amounts of feces. Combine that with the relatively large amount of urine produced by Oscars, and you have substantial hurdles for both biological and mechanical filtration.
A second consideration is the size of the tank. If you need help selecting an apropriate sized tank, read this article, and this article. Larger tanks will need more filtration, both to provide adequate water movement, and to ensure that all water in the tank passes through the filtration with a reasonable frequency.
A third consideration is your budget. Different types of filters cost varying amounts. However, as we will examine later in this article, the old axim “you get what you pay for” is quite true in fishkeeping.
Types of filters and their usefulness in Oscar keeping
When I talk about wet/dry filtration, I am talking about sumps that sit under the tank, not the “bio-wheel” filters produced by Marineland. Wet/dry filters are the kings of biological filtration. They achive this superior biological filtration by running water across massive amounts of biological media in the presence of air. Different designs achieve this in different ways, but the principles involved remain the same. The only drawback of wet/dry filters is that they normally either lack, or are very weak in the area of mechanical filtration.
As mentioned above, mechanical filtration is quite important in an oscar tank. Therefore, if you use a wet/dry set-up, you will need to make sure that mechanical filtration is covered. This can be done by either modifying your wet/dry system to include mechanical filtration directly, or by adding supplemental filters to perform the mechanical filtration role.
Modern cannisters are the Jacks-of-all-trades of the filtration world. They do this by providing large amounts of space for media that can be customized to fit your specific needs. They can be optimized to provide mainly biological, mainly mechanical, or a good balance between the two.
Cannisters are also excellent investments because of their ease of maintenance, and relatively inexpensive operating costs. Properly-sized cannisters can go anywhere from a month to as much as 4 months without any maintenance. Compare this to most other types of filtration, which needs to be serviced at least every couple of weeks, and you can see some substantial savings in bot time, and media costs.
Also called Hang-On-the-Back, or HOB filters, the power filters are by far the cheapest filters to buy. They are an excellent choice for smaller (55 gallons and under) tanks, or as supplemental and/or back-up filtration on a larger tank. While it is theoretically possible to put enough HOB filters on tanks up to about 125 gallons to provide adequate filtration, I do not recommend it. This is because in this size range, you are talking about at least three filtes that will most likely need to be maintained weekly. This is an aweful lot of work and recurring expense for filters that are only marginally adequate.
While it would be difficult to add enough to properly filter a tank with one or more full-grown oscars, sponge filters do have some good uses in Oscar keeping. They are a cheap way to add a little extra mechanical and biological filtration to a tank, and make nice back-up filters. Also, if you keep one running in a large tank, you have a pre-cycled filter ready if you need to set-up a hospital tank. Sponge filters are also cheap, effective filters for fry grow-out tanks.
Two factors essentially rule out undergravel filters (uGFs) for oscar tanks. First is the general messiness of Oscars, which is discussed above. The waste tends to clog up the gravel, and reduce the flow through your UGF. Second, Oscars love to dig, especially around spawning time. They dig so much that they will often dig all the way to the bottom of the gravel, and expose the UGF’s plates. This will cause a short-circuit in the water flow, and virtually eliminate any filtration occuring in the UGF. When combining these two factors, it is generally best to avoid UGfs in an Oscar tank. While they might provide some benefit as supplemental filtration, the work involved in keeping the gravel clean and the UGF plates covered is simply not worth it.
Selecting Filters for a Specific Tank
When it comes down to selecting specific filter models for a specific tank, there are many combinations that will “work” the actual filters you will choose will depend heavily on your personal preference, and the amount of money you have to spend. With that in mind, I am going to talk about some specific examples, along with filtration combinations that will work in the situation given. The filtration recommendations are listed in order of decreasing initial cost, and increasing work and recurring cost. I specify filter types generically, in terms of a filter type, and size. I will use the following general categories:
Medium Cannister: Eheim 2235, Eheim 2215, Ehiem 2071, Filstar XP2, Fluval 305, Marineland C-220
Large Cannister: Eheim 2026 (or 2126 if you want a built-in heater), Eheim 2217, Eheim, 2075, Eheim 2074, Eheim 2076, Filstar XP3, Fluval 405, Marineland C-360,
X-Large Cannister: Eheim 2028 (or 2128 if you want a built-in heater), Eheim 2080 (or 2180 if you want a built-in heater), Marineland C-360,
XX-Large Cannister: Eheim 2260, Eheim 2250, Fluval FX5
Large HOB: Aquaclear 110, Emperor 400, Penguin 350B
Wet/Dry: I do not have any personal experienced with wet/dry filters, so I will have to leave the specification up to your research.
Note that I strongly believe that any Oscar tank should have at least two filters, even if the second filter is not strictly needed for basic filtration. This is so that there is a back-up in place if one filter fails. With a fish as messy as an adult Oscar, pollutants will build up fairly quickly if there is no filtration on the tank. Having that back-up in place may mean the difference between a minor inconvienience and a major disaster. Even if I dont mention more than one filter in a particular setup (because it is not strictly necessary), I would strongly recommend adding a large HOB to any single-filter set up as a back-up.
Specific Filtration Recommendations
Setup 1 – 55 gallon tank with one adult oscar
Medium cannister plus Large HOB – This is optimal for a 55.
Two large HOBs – will be a little more work, but will still provide excellent filtration.
Setup 2 – 75 gallon tank with 2 adult oscars
Large Cannister plus Large HOB – Optimal.
Medium Cannister plus Large HOB – This will still do the trick on a 75, but you will have a little more maintenance on the cannister.
Two large HOBs – This is getting to the point where two HOBs are only marginally adequate. They will need to be cleaned frequently, and water changes will need to be more frequent, but it can be done.
Setup 3 – 125 gallon tank with 2 adult oscars plus a few “friends”
Wet/Dry – This is the tank size range where the cost of a Wet/dry set-up starts to make sense. Remember to make sure that there is adequate mechanical filtration.
Two Large Cannisters
One X-Large Cannister Plus Two Large HOBs
Three Large HOBs – Again, this will only provide marginally adequate filtration, and will mean a lot more work.
Setup 4 – 180 gallon tank with 2 or more adult oscars, and several “friends”
One XX-Large cannister
Two X-large Cannisters
One X-Large Cannister plus Three Large HOBs