JBL CristalProfi e1902 GreenLine UK Plug is the largest external filter in JBL's CristalProfi e range, for tanks of 200 to 800 litres and roughly 120 to 150cm long. JBL rates the pump at 1900 litres an hour and the filtration capacity at 15 litres, which is a great deal of media to put behind a tank.

Key Features

• For aquariums of 200 to 800 litres: JBL's figure for this model, and the first thing to match before anything else.
• Suits tanks around 120 to 150cm: JBL gives a length as well as a volume, which is the better guide when a tank is tall or shallow.
• 1900 litres an hour pump: JBL's rated output. In practice you will see less once media and hose are in the way.
• Quick-start priming button: the filter primes itself at the push of a button instead of you sucking on a hose, which is the job everyone dreads.
• Patented pre-filter: JBL's pre-filter catches the coarse dirt first, so the biological media behind it stays clear for far longer.
• Closed water circuit: the water leaves the tank, goes through the filter and comes back, which is what lets an external hold so much media.

Setting Up An External Filter

• The filter body has to stand below the water line, in the cabinet rather than beside the tank. An external filter is a siphon with a pump in it, and it will not prime above the water.
• Keep the hose runs as short and as straight as you can. Every extra metre and every tight bend costs you flow.
• Check both hose connections and the head seal before you switch on, then look again an hour later. Leaks show up on the second check, not the first.
• Never let it run dry. A pump with no water in it will destroy its own impeller and shaft in minutes.
• Put the coarse foam first in the flow, the fine foam after it and the biological media last. Fine media placed first simply blocks.
• Keep a towel and a bucket under the cabinet whenever you open it.

Good To Know

• A new filter has no bacteria in it. Stock slowly over the first weeks, feed lightly, and test ammonia and nitrite until both read zero. A filter becomes a filter over about a month.
• A pump's rated output is measured with nothing in the way. Media, hose length and height all reduce it, so the figure on the box is a ceiling rather than what you will see.
• Rinse filter media in tank water, never under the tap. Chlorine kills the bacteria that do the biological work, and that is most of what a mature filter is worth.
• Service before the flow drops noticeably. By the time you can see a filter struggling it has already stopped doing part of its job.
• Never replace all the media at once. Change one stage at a time with a week or two between, or the tank can cycle all over again.
• Switch the filter off at the mains before opening it or putting a hand in the tank, and fit the cable so water cannot run down it to the socket.
• JBL gives a two-year guarantee, extended by a further two years if you register the filter with them.
• Service the pre-filter more often than the rest. That is the stage doing the dirty work, and keeping it clean is what keeps the biological media working.