http://www.ebay.co.uk/itm/230653926927?ru=http%3A%2F%2Fwww.ebay.co.uk%3A80%2Fsch%2Fi.html%3F_from%3DR40%26_trksid%3Dp5197.m570.l1313%26_nkw%3D230653926927%26_sacat%3DSee-All-Categories%26_fvi%3D1&_rdc=1#ht_1675wt_1037
here is the skimmer im looking at. i worked it out that the tank will be able to hold 160L but with all the rock im going to be put in it will only be holding about 120-130L.. is this not good for me
if not could you point me in the right direction please
I would just base it off how big the tank is, and not how much water you think you will actually have. You really can't get a skimmer that is too big.
I didn't realize you are in the UK, so that will change what is available to you.
I am not familiar with this brand, so I can't tell you how well it works. The price leads me to believe that it won't work well. I have found that skimmers are definitely something that you get what you pay for and the more you spend the better it works(within reason).
Here are some options I found on UK Ebay:
1.
http://www.ebay.co.uk/itm/Hang-Prot...upplies_Fish&hash=item27c0dd2c21#ht_490wt_833
This is the best skimmer of the 3 options here, but is the most expensive, is used, needs a pump and a rubber ring that goes around the collection cup, and has a crack that would need some epoxy.
2.
http://www.ebay.co.uk/itm/Aquarium-...pplies_Fish&hash=item5d31132f51#ht_1773wt_982
This one is cheaper and looks like a Coralife skimmer. It is new and includes pump and is rated for well bigger than your tank size which is good.
3.
http://www.ebay.co.uk/itm/Red-Sea-P...upplies_Fish&hash=item2316e89ad5#ht_500wt_902
This one is still small for your tank, but bigger than the one you posted. It is used, but very cheap and includes pump.
Of these three options, the 1st is easily the best skimmer, but obviously there are quite a few things you would need and it is quite pricey. I think if I had to choose between these 3 options I would go with number 2. It is up to you and there are more choices out there, this was just a sampling.