how many fish did you buy petplanet? 2 or 3 ??
years (20 or so) ago i had a tank around 80 ltr. was huge for a beginner then, with 11 fish including emperor angel. all but one died on white spot!!!
i almost gave up saltwater then! i got no advise on feef keeping then!!
having keept marines for over 2 decades now i have to admit that some things have improved to the better, esp. for SPS corals.
others might be losing out like catalaphylia, goniopora,some LPS etc. i agree with you that it is still possible to have a reasonable saltwater tank (not reef tank) on a low budget, but would recommend newbees to invest as much as their pocket allows on lighting, tank size etc. because what you reallu want is something to be proud of and be able to show to your friends. and a 20 litr nemo tank with 2 clown fish and some rock doesn't quite cut it!!!!! and if it not for your friends its for your inner self, it makes you feel great to look at a living reef, not a couple poor fish swimming around a silly rock in a 20 ltr tank. i haven't lost many fish over the last ten years, next to what my box fish killed off, and i put it down to knowledge, experience and the right setup. what ever that may be!!!