yeah unfortunately the only difficult bit of fishkeeping really is getting it started up properly, once you're off the ground it's plain sailing so don't panic if this all sounds hideously complicated.
what the fish shops don't bother to tell you is that the filter they have sold you is basically just hardware, it's like a computer without windows installed on it..... not a lot of good to most people! What you need to do is 'install' two species of bacteria on the filter media. Basically the fish produce ammonia as their waste, you need the first species of bacteria which we'll refer to as 'A-Bacs' to consume all that ammonia and convert it into nitrite, unfortunately the nitrite is also toxic to fish so you need a second bacteria species called the 'N-Bacs' which will convert the nitrite to nitrate. Nitrate is only toxic in massively high doses so you just remove this with weekly water changes.
We advise people to go through a process called fishless cycling, this basically simulates fish being in the tank by adding ammonia to it over a few weeks, the bacteria colonies that you need will grow up and then when you come to add fish the bacteria are all there for you to deal with the fishes waste so the water is safe.
The bacteria product you have been sold is trying to miss out this step by just conaining a load of the bacteria which you can dump into your tanka dn then just add fish, nice little idea. It's just a shame that they don't work! There's very little regulation of aquarium products so unfortunately they do not all do what they claim to do which (as you can imagine) is very frustrating for us hobbyists. You think you've done everything right and then you're thrown into this dodgy situation.
Now you're friend is very close to the solution for you, as her tank has been running for months/years it will almost certainly have nice strong colonies of both these bacteria species living in the filter media. So if you can get a chunk of sponge from her filter and pop it into yours then you'll bring over a nice colony of bacteria and the water quality will be fixed in hopeful;ly a few days rather than aking several weeks as you would expect if you didn't get the media from her filter. She's just made a common misconception that the bacteria are in the water, they're not a free-swimming species they cling onto surfaces so while there emay be a minimal amount in the water it won't make any difference to move it to your tank, but in her filter in the sponges or whatever else she's got in there she'll have loads and loads of lovely bacteria which you can move to your tank.
Without a shadow of a doubt this is your best course of action, for 6 neons you won't need that much media, take no more than one third of the total that she has, it's polite in these circumstances to buy some new media to replace her's with. bag it up in a sealed bag or tupperware with water from her fish tank (not tap water) and get it into your filter within 24hrs (although quicker is better) making sure that it never dries out.
Now - onto the other stuff, don't worry about the bubble curtain, your make of filter provides plenty of oxygen, if you like the look of them then by all means get one but there's no practical need to, it won't change things.
What you do need to get now is a new test kit, the test strips are notoriously unreliable as you can see from the difference between your readings. If you look for the API FreshWater master Test Kit this contains everything you need. The fish shop may sell it or alternatively it's always available on ebay for around £20.
In the mean time we have no idea what your water readings actually are, so it's safest to assume the worst, if you can do a large water change every day with fresh dechlorinated tap water then this will hopefully keep the water clean until you get a test kit and the mature media sorted from your friend and we can then start to work out what's really going on.
Right I think that's enough info to bombard you with at one time, so hit me back with any more questions.
