Review: Ocean Free Hydra 30 internal filter


Nathan Hill reviews a new filter that makes some big claims.

Why, oh why, do companies that have a potentially brilliant idea try to hide it with shameless marketing jingles and words that have less value than a Monopoly game pound note?

The Hydra 30 is said to use 'Hydro-Pure Technology' — which tells us nothing about what it does. In fact, the chart it then uses to try to show us how ‘Hydro-Pure’ works makes as much sense as a trolley filled with badgers.

Without going into too much scientific jargon, from what I understand of it there’s a part of the filter that appears to be dedicated to the generation of hydroxyl radicals. I could be wrong, as the information associated with the product is vague at best, but if that’s the case there’s no need to give it a fancy-sounding name.

After all, hydroxyl radicals are incredibly reactive and will oxidise all manner of waste — in a way much like a poor man’s ozoniser.

If it does what it claims to do, I have no reason to doubt that some biological waste will be removed through this process, but I’m wary at just how much of it is oxidised.

Many charts duly appear in the instructions, purportedly showing the results of ‘a test’ to illustrate how great the filter is. If you want to accept those figures as gospel, then on your head be it.

To work, a catalyst block is included, which the packaging assures me is not carbon, despite looking, smelling and tasting like carbon. The lifespan of the catalyst isn’t stated, nor, worryingly, are the implications of running the device without it.

Big claims are made regarding filter capacity, with the ‘30’ model rated for between 100-300 l/22-66 gal aquaria.

With a flow rate of between 500-550 lph, you’d have decide how to play that, but I’d have it in a tank of up to 200 l/44 gal or so.

There’s also a curious 'anaerobic chamber' to which the aquarist can add media of his or her choice, or leave blank. I’m incredibly twitchy about anything claiming anaerobic properties, especially when they are totally unregulated, as in this case.

As for the usual criteria, I like the filter a lot. It’s easy to work with and a lot sturdier than some I’ve seen of late. The design is classical and unimposing, so if worried about the thing sticking out then don’t be. It’s very inoffensive.

Cleaning is a little more than a usual internal task, as not only do you need to clean media but you’ll also need to keep the reactive plate —a rectangular clearing at the front of the filter which you'll need to dismantle to reach — spotless if to keep it all working.

Check the plug, if you’re buying one, as mine came with a non-UK two-pin and I detest swapping plugs. It’s not really an energy guzzler, at just 13w in total, but, even so, correct plugs would be nice.


I want to love it, but the makers need to be a lot more transparent about exactly what it does and how. Give me the science — not just a couple of shaky charts and meaningless words. I'm hoping to see something special for the price.

Price: Approximately £59.99, from

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