Oase BioMaster 250 vs 350: Canister Filter Comparison

I'll take you through the differences between the BioMaster 250 and the BioMaster 350 so you can decide which of these premium filters is the right one for you and your fish tank setup.
Oase BioMaster 250 vs 350

Italian-built with German engineering, Oase BioMasters are not the cheapest canister filters out there. But, as the old saying goes, you get what you pay for.

So, without further ado, let’s get to it.

Oase BioMaster 250 vs 350

If you’re in a rush and just want to know all the essential info it’s summarized below, with a more detailed comparison further down.

You may notice my tank size suitability figures differ slightly from what Oase states. I’ve done a chart further down explaining how I work this out.

Tank Size Up to 50 Gallons (190 Liters) Up to 70 Gallons (260 Litres)
Pump Output250 G/ph (950 L/h)350 G/ph (1,300 L/h)
Filter Media Capacity4 baskets holding 1.3 gallons (4.8 liters)5 baskets holding 1.6 gallons (6.1 liters)
Power Consumption120V – 15 Watts / 240 Volts – 15 Watts120 Volts – 16 Watts / 240 Volts – 18 Watts
Annual Running Cost (Approx)$15.77$16.82
DimensionsH 14.6” x L 9.4” x W 9.4”H 16.7” x L 9.4” x W 9.4”
Filter Media Included4 x pre-filter foam pads, 1 x 30 ppi orange coarse foam filter pad, 2 x 20 ppi blue ultra coarse foam filter pads, and 1 bag of Hel-X biomedia5 x pre-filter foam pads, 1 x 30 ppi orange coarse foam filter pad, 3 x 20 ppi blue ultra coarse foam filter pads, and 1 bag of Hel-X biomedia

The entire BioMaster series filters are a breeze to set up and maintain (details and tips on how to do this further down).

Oase BioMaster 250 vs 350 Dimensions

They come with 3 year warranty, plus an additional year’s warranty when you register your purchase with Oase.

They are also retrofittable with an Oase heater which upgrades them to a BioMaster Thermo filter, which is a really great feature as the heater goes inside the filter, so you don’t have to have an ugly heater inside your aquarium.

Here is a quick overview of all the essential info:

  • Tank size: The Oase BioMaster 250 canister filter is suitable for tanks up to 50 gallons (190 liters), while the Oase BioMaster 350 is designed for tanks up to 70 gallons (260 liters).

  • Size: Both filters have the same footprint, but the BioMaster 350 is 2.1” taller than the 250, so if you’re tight on space you may struggle to fit it beneath an aquarium.

  • Filtration capacity: The BioMaster 350 offers a higher filtration capacity with a circulation rate of 350 gph compared to the 250’s 250 gph.

  • Energy efficiency: Both the 250 and 350 are super energy-efficient options that can potentially save you money on your bills in the long run, compared to older less efficient filters.

    Based on a cost of $0.12 per kWh, the runnings costs for each filter are:

    BioMaster 250 = $15.77 per year.

    BioMaster 350 = $16.82 per year.

  • Tank Stocking Levels: If you have a heavily stocked tank, it’s best to choose a more powerful filter to keep the water clean and clear. Use the chart below to work out what flow rate you need for your setup.
Oase Biomaster 250
Oase BioMaster 350

What Size Canister Filter Do I Need?

A general rule of thumb is that you want the pump output (gallons per hour) to be 5 times the size of your tank, so multiply the size of your tank by 5 to find out the g/ph that is ideal.

I’ve found that following this simple calculation stops you from buying a filter that is too small or too large (and wasting money) for your aquarium.

If you have an overstocked stocked tank that has a large bioload, it’s recommended that you multiply your tank size in gallons by 10, to find a suitable turnover rate for your tank.

Since there is no standardized calculation used by all the different manufacturers, each manufacturer may suggest a different tank size suitability for their ‘XXX g/ph’ filter.

By using this formula, you can compare filters from different manufacturers on an equal basis.

20 100 g/ph 200 g/ph
29 145 g/ph 290 g/ph
40 200 g/ph 400 g/ph
55 275 g/ph 550 g/ph
75 375 g/ph 750 g/ph
90 450 g/ph 900 g/ph
100 500 g/ph 1000 g/ph

Most manufacturers state the g/ph when the filter is empty with no media in place. 

Once the media is in place (and it’s got gunked up after a while!), these g/ph figures reduce drastically and the real-world turnover rate will probably be around 50% less. 

Nonetheless, I’ve found on the whole that the filtration based on this calculation is more than adequate.

Oase BioMaster 250 vs 350: Detailed Comparison, Setup Guide, Maintenance & Tips

Now for those of you who like to know every last detail, grab yourself a drink and get comfortable, we’ll dive into all the differences in more detail. 

I’ll also cover how to set up the filter, maintain it, and include some handy tips along the way.

Tank Size

Oase BioMaster 250 is suitable for aquariums of up to 50 gallons (190 liters).

Oase BioMaster 350 is suitable for aquariums of up to 70 gallons (260 liters).

The BioMaster series also has 2 larger filters available, the BioMaster 600 and the BioMaster Thermo 850.

Type Of Fish You Keep

Different fish require different levels of filtration. Some fish are particularly messy so you need to make sure your filter can cope with them. 

I’ll list a few common messy fish and if you keep any of these guys you may be best choosing the 350 because it has an extra basket for filter media to help catch all the additional mess, to keep your water sparkling clean and clear.

Bristlenosed Plecos – Although these guys are part of a tank’s clean-up crew and do a great job of eating algae and leftover food, all that algae and food have to come out the other end and they are known to be pooping machines!

Cichlids – In particular large cichlids like Oscars, who are known to rip up plants, stir up the substrate, and even re-arrange rocks, all creating lots of mess.

Goldfish – These guys love to dig around and stir up the substrate and are known for pooping a lot, so you need a filter that can cope.

Turtle – If you keep a turtle rather than fish in your aquarium, you will need a much more powerful filter to deal with the amount of waste they produce, check out my turtle filter guide for more info.

Freshwater and Saltwater Compatibility

Both the BioMaster 250 and 350 external canister filters are designed to work in freshwater and saltwater aquariums.

Filter Media

Oases BioMaster Filter Media

Both filters come with filter media included, consisting of mechanical, biological, and chemical filtration.

The BioMaster uses a series of foam pads, but you could choose to replace these with other filter media if you wish.

I’d replace 1 or 2 of the blue foam pads with some extra biological media, Seachem Matrix is a great choice and what I use.

SeaChem Matrix

The BioMaster 350 comes with 1 extra pre-filter pad and 1 extra blue ultra coarse foam pad.

Oase BioMaster 250 and 350 Setup

Setting up the BioMaster 250 and 350 is the same process.

When you open the box, you’ll find the main canister body, which has all of the filter media already in place inside the canister, and a box containing:

  • Inlet assembly – comes in 4 separate parts
  • Outflow assembly – comes in 2 parts
  • Outflow spout
  • Output spray bar – comes in 4 separate parts
  • Thermostat cap
  • 1 x 13’1.5″ (4 meters) hose
  • 4 x hose connectors
  • 4 x clips
  • 4 x suction cups
  • 4 x rubber feet – for under the canister body
  • Instruction manual
  • Warranty leaflet


The first thing you’ll notice lifting the filter out of the box is it comes with a carry handle and feels really well-made and robust. Whoever thought to add a carry handle is a genius….please take note Fluval!

If you’ve had a canister filter before you’ll know all too well they can be quite heavy and cumbersome to handle, especially if you have them in a confined space. The handle makes handling this filter so much easier.

The first thing I do is take the canister apart and make sure everything is inside.

You’ll notice 4 large blue clips, one on each side of the filter. Before you lift the clips you’ll have to raise the handle first as there’s a small lug that stops you from unfastening the side clips by accident.

Oase BioMaster Lift Handle Security Tab

Depending on which model you have you will have either 4 or 5 baskets inside. 

Apart from the bottom basket, each should have a foam pad inside. The top basket will have an orange fine foam pad and the other baskets will have coarse blue foam pads.

The bottom basket should have a net with some white plastic things inside, this is your Hel-X Biomedia.

Once you’ve confirmed everything is present, you can put the baskets back into the canister, refit the head and fasten the 4 clips back in place.

Next, check your prefilter sponges are in place. Slide the blue water flow lever to the unlock position, then slide the blue pre-filter lever to the unlock position and lift the pre-filter out.

Locate the 2 tabs on the grey plastic cover, press them in and the cover should just slide off. Once you’ve confirmed your sponges are present, refitting it is the reverse of removal.

Fit the 4 rubber feet in the corners on the underside of the canister and fit the thermostat cap, or heater if you got the BioMaster Thermo, when fitting the heater it’s quite a snug fit so you’ll have to push it in firmly.

Position the intake and outputs where you want them in your tank.


Place the filter on a flat and sturdy surface, beneath your fish tank.

Canister filters are ‘gravity fed’ so they need to be below the tank for them to work correctly. If you put a canister filter at the side of a tank, the top of the filter must be below the surface of the water, but it can be tricky to get the filter working efficiently.

Position the filter as close to your aquarium as you can and avoid any sharp bends or turns in the tubing.

Fit The Tubing

The hose is supplied in a single length that you have to cut yourself.

The tubing seems like it has a mind of its own, so to make the tubing easier to work with, soak it in a sink full of hot water for 5 minutes.

To avoid miscutting my pipe the wrong length (come on, we’ve all done it!) I find it easier to attach both ends of the pipe to the filter valves at this point, then cut it once I know it will reach over the top of the tank and back into the water.

The intake and output valves on the filter are clearly marked so you can easily tell them apart.

The intake and output brackets have an adjustable water flow dial (see image below) which is a great feature and ensures you can get the perfect water flow rate for the type of fish you have.

The filter comes with a spray bar (clear tubes with holes in) which can be attached to the output nozzle. Don’t forget to add the cap to the end.

Alternatively, there’s a duckbill-shaped attachment if you don’t want to use the spray bar.


To prime the pump: 

  1. Ensure your output nozzle is above the water’s surface so it has access to air.
  2. Press the blue button on top of the pre-filter down and hold it in place for a few seconds until it starts drawing the tank water in.

Once the canister filter has filled with water, plug it into the mains power and you should have water flowing out of the outlet nozzle.

Leave it running for a while as it will take several minutes to get all of the trapped air from the sponges and out of the canister.

I always recommend having a drip loop on all electrical items for your aquarium, we all know water and electricity are not a good match!

Aquarium Drip Loop

That’s it, you’re all set up and good to go.

Maintenance and Cleaning

It is the same process for cleaning both the 250 and 350.

This is where the Oase filters really come into their own, because they have a separate pre-filter section it makes cleaning a breeze compared to other canister filters and is a big time saver….which is always a bonus!

The pre-filter sponges do such a great job of catching the majority of waste, so the filter media in the main compartment doesn’t get clogged up and dirty quickly, meaning you can go longer between having to clean the main compartment.

If you clean the pre-filter sponges on a weekly basis, it will only take 5 minutes and it could be months before you need to clean the main compartment.

Pre-Filter Cleaning

Unplug the filter (and heater if you have one fitted in your filter).

Slide the water flow lever to the unlock position, then slide the pre-filter lever to the unlock position. The pre-filter will now lift out.

Unclip the prefilter cover and remove the pre-filter sponges and clean them, you can do this under the tap as the majority of the beneficial bacteria will be inside the main compartment of your filter.

Using a bottle brush, give the intake and output holes of the priming head a clean, and don’t forget to scrub the inside of the tube that goes through the prefilter sponges.

1" Bottle Brush

When you put the pre-filter section back into the canister, press it in very gently or you’ll force water out of the canister and all over the floor – I’m not telling you this from experience, honest!

Main Canister Cleaning

This won’t need to be done very often if you keep on top of cleaning the pre-filter sponges. 

The only downside to this filter is that I wish it had a handle that lifted all the media baskets out in one go, like on the Fluval 07 range, but it’s not a huge deal breaker.

Unplug the filter (and heater if you have one fitted).

Let the heater cool down for 15 minutes before removing the filter head.
If you remove the heater from the water while it’s still hot, it could cause it to crack.

Slide the water flow lever to the unlock position and detach the intake and outlet valve assembly.

Raise the lifting handle and unfasten all 4 blue EasyClick clips.

Lift the filter head vertically, being mindful not to damage the heater.

Put a towel and bucket on the floor and empty the water from the filter into the bucket, you’ll then use this water to clean everything.

Remove each basket and rinse out the sponges, or any other media you’re using.

Clean the main body of the canister where the filters go: Add a bit of water and swish it around to loosen any brown sludge in the bottom and pour it into the bucket.

Clean the impeller and housing. The impeller is located in the right rear corner of the filter head, the cover twists off in either direction. Something I really like is the impeller tips are made of hardened plastic with 2 rubber bands bound around them which are much more durable than the all rubber tips you normally find on canister filters.

Reassemble and reconnect the filter, then prime it.

Once it’s filled with water you can plug it back into your mains power and off it goes.

Use the water in the bucket to water your garden or house plants, they’ll love it!

Pump Performance and Efficiency

When you’re looking to choose a new canister filter, the filter’s pump performance and energy consumption are important things to consider with the ever-increasing cost of living.

Pump Output and Circulation

The BioMaster 250 has a filter circulation rate of 250 gallons per hour (950 L/h), making it suitable for aquariums of up to 50 gallons (190 liters).

On the other hand, the BioMaster 350 has a higher filter circulation rate of 350 Gal/h (1,300 L/h), making it suitable for aquariums of up to 70 gallons (260 liters) or for a heavily stocked smaller aquarium.

Energy Efficiency

Oase BioMaster 250 vs 350 Energy Efficiency

With ever-rising energy prices, this has to be something to take into consideration.

Both BioMaster filters excel in energy efficiency.

The 250’s power consumption is 120 Volts – 15 Watts / 240 Volts – 15 Watts

The 350’s power consumption is 120 Volts – 16 Watts / 240 Volts – 18 Watts

According to the energy.gov website, at the time of writing, the annual running cost of each filter is:

  • BioMaster 250 at the US Average of $0.12 per kWh = $15.77 per year
  • BioMaster 350 at the US Average of $0.12 per kWh = $16.82 per year

Filter Noise

I’m really sensitive to background noises, the slightest little thing drives me nuts if I’m trying to read or watch TV.

The BioMasters are super quiet and come in at around 44 decibels.

Damn, that’s quieter than my Fluval 407!


The 250 is the smaller of the 2 filters so is more budget-friendly.

Oase BioMaster 250
Oase BioMaster 350

What’s The Difference Between Oase BioMaster and Oase BioMaster Thermo?

They are the exact same filter. The only difference is you get a heater included with the BioMaster Thermo.

I like this as it offers us fishkeepers a bit of flexibility.

Let’s say you want to keep goldfish now, but at some point in the future you decide to get tropical fish that require warm water, you can buy the tank heater separately and retrofit it to your BioMaster filter.

Another major benefit of this is it’s one less piece of unsightly equipment inside your tank and you don’t have to risk your fish burning themselves.

The heater for the BioMaster 250 is the Oase HeatUp 150

Oase HeatUp 150

The heater for the BioMaster 350 is the Oase HeatUp 200

Oase HeatUp 200

Conclusion – Oase 250 or 350 Which Should You Buy?

You’ll be super happy with the Oase BioMaster filters and I can highly recommend them to you. They’re reliable, super quiet, easy to maintain and cheap to run, so which should you buy?

If you have an aquarium of up to 50 gallons, buy the 250.

If you have an aquarium that is 50-70 gallons, buy the 350.

Check out the equipment section for more comparisons and setup guides like this one, and the aquarium health section for guides on keeping your finned friends happy and healthy.



Hey, fellow fish enthusiast 👋! I'm Paul and I've been an aquarium addict since I won my first goldfish at the fair many years ago. Let me share with you the knowledge that I've gained along the way (and avoid the mistakes I've made!), so you too can create an underwater paradise for your aquatic friends.