Should I Have Two Filters?

Ideally you are looking to have a turnover of around 5 times tank volume per hour, so in your case 450 litres per hour. If yours has 1800 l/h turnover, that is 20 times the tank volume per hour, which is more than enough. In fact I'd be more worried about turning the tank into a whirlpool. Can you adjust the flow rate of the filter?

Though I just noticed you said drip filter - can you explain what you mean by that please - is it one of those filters that are in the hood rather than inside the tank?

Can I also ask what is inside the filter - sponges, ceramics, cartridges etc?

This sounds a lot like one of my tanks, an Aqua-one AR620 which has the same type of filter. I've found it to be an excellent filter, plenty of media for the size of tank, but it is certainly not 1800 L/H. just a sensible rate for the size of the tank.

Thanks, guess i'll wait till im up and running and see if it's ok or like the wake of a speedboat lol. I was also sold some K1 Media plastic stuff to place under my sponge mat but from my many googles, it looks to me like K1 is meant to be used on it's own to move freely, surely under sponge it won't do that?

Don't use the K1 plastic stuff. As you say - that's for huge moving-bed filters, the sort you'd have in outdoor Koi ponds.

If you can get some ceramic or scintered media then that would be best. I use this stuff. Excellent, IMHO.