First of all, it's not your fault, you never heard about cycling.
Is the tank 620 litres? If so, that's great, you have lots of space, which is a good thing.
N
ow, have a look on this forum and around the internet, you should find an article on fish-in cycling. it's more dangerous than fishless, but, since that, you have no other choice, other than to take back the gouramis.
Now, the Neon Tetra problem.
Neon Tetras are VERY VERY sensitive fish, not suprised that they did die, because of no cycling.
They should be added around 2 weeks after cycling's been finished.
Now to the brown algae.
I am having a huge problem with it in my tank, no worries.
It usually happens on New tank setups because of the Phosphate and Carbon molecules. It is not harmful to your fish. In fact, my fish always nibble on it.
My best advice for this, is cutting down feeding a little bit, to about 1-2 times a day with treats every 3-7 days.
thanks for your reply, i think the tank is 90 litres, its 24 inches wide x 14 deep x 17 high. its not massive but its all we have room for..... i have been told that the amount of fish is 1cm of fish for 1 litre of water, is this correct? not that im ready for any more fish yet but it would br nice to know when planning what fish to add.... i will check out the fish-in cycle, cheers. Matt
To get rid of it, you can use a very clean cloth (No soaps in it, or anything) and wipe it down. If you have the money, you can go to your LFS, or even Wal-Mart, and go buy an Algae Scrubber, they are pretty useful, they sell for around $10.
Hope I helped.