Marine fish keeping doesnt need to be expensive or complicated hobby. If you stick to your budget then marine fish keeping can be a hobby that you can enjoy. You can easily keep a Nano Reef Aquarium without having to buy Fluidised Filters, Calcium Reactors and Nitrate Filters.
If your looking to get a small fish tank then an fluval roma 90 can be bought for just over £200, and it has all the basic equipment that you will need such as UV Steraliser and a Protein Skimmer, but due to the size of the fluval roma 90, you will be limited to what types of fish you can keep, so unless you are planning an upgrade then you won’t be able to keep fish like Regal Tangs, Flame Angels and Picasso Tangs.
If your looking to keep these types of marine fish then your going to need to aqquire a larger tank over 300 litres preferably. Then you are going to need to buy some extra equipment like Power Heads and Protein Skimmers. But if your Aquarium has a sump underneath then its easyier to place all these peices of eqiupment and they can be hidden out of sight.
If you have a sump located under your tank then you can place any extra filters in there and hang UV steralizers on the rear of your cabinet.
Certain types of marine fish need to be placed into mature aquariums such as Cobberband’s which are also notorious for been difficult to get feeding, so these aren't recommended for people new to the marine fish keeping hobby.
If your unsure then you can always ask your local fish shop or check on line for reef compatibility of the marine fish that takes your fancy.