Outside Filters

With that sized tank, definitely go for an external. The Rolls Royce of external filters are by Fluval and Eheim.

You'll find the Fluval range here https://uk.hagen.com/Aquatic/Filtration/External?brand=Fluval with the manuals in the Useful Tools menu at the top of the page - I always read the manual before buying anything from filters to tumble dryers 
Eheim filters here https://www.eheim.com/en_GB/products/technology/external-filters with manuals given in the downloads section with the technical specs for each type of filter.

I can't comment on externals from personal experience as I have internals, but other members have externals and can tell you which brands they like and why.



One thing I do know about externals is that you can customise the media, you don't have to use what they give you. For example, most of them come with carbon, either a bag of granules or impregnated in a sponge. You don't actually need carbon. Keep some in the cupboard in case you ever have to medicate the tank and need to remove the med afterwards, and fill the space in the filter with sponge or ceramic media.

Hi
Thank you both. Its given me some food for thought.
Steve D

i have a Juwel 400 with a built in internal and I have a betta 2000 LPH with I tray with sponges and 3 trays of ultimate bio-home, had it running for 3 months shows under 0.25 ammonia but my tap water shows 0.25, nitrite .0 my nitrite has always been high but have now started dropping.