[Rusalka]

A similar thing happened to me a few months ago and it settled pretty quickly with a week of monitoring and 50% water changes as neccessary.

The yellowish tinge is likely tannins leaching from your soil and it is nothing to worry about, unless you don't like the look of it - in which case you could add a little activated charcoal to your filter. Actually your betta probably loves it, as tannis are often present in their native environment.

As for the cloudiness that is also often normal in a new tank - however, i've noticed that sometimes it accompanies high nitrite levels in a tank (as it did in mine). Some people have used miracle grow on this forum with good results, but it may have artificially added nutrients that will temporarily throw the balance off. Keep monitoring your levels and doing water changes as neccessary.

As for your fern - maybe the light is too high? Once I moved mine into a shadier area it came to life.

 

[Rusalka]

In an NPT you generally want to avoid too much splashing or disturbing the surface of the water as it encourages CO2 to dissipate into the air - and your plants will not have any left to photosynthesize with during the day. This will cause very slow growth and perhaps may be contributing to the problems some of your plants are having. You should not be having any problems with dangerously low oxygen levels in your tank as it would have to be absolutely exploding with plant life to be suffocating your fish. The gasping you were seeing was most likely a symptom of nitrite poisoning, especially since you did have elevated levels. I hope all settles down nicely!

 

[Rusalka]

Yes you are right the plants DO oxygenate the water - don't let me confuse you on this! I was getting a little ahead of things and thought the reason you were adding aeration was because you were worried that the plants would not be producing oxygen at night - but reading back I think you were referring to a specific night - do I have that right now?

Here's a mini explanation of the rest of my post. Plants can take up O2 at night - that's why I mentioned that if your tank was absolutely plugged with plants, it could in theory reduce O2 levels to a low level. I'm not sure about how many plants this would require - but I imagine it would take so many that your fish would have nowhere to swim! Maybe one of the moderators or senior members can give us some more specifics on this?

Also, you should give Diana Walstad's book a look-see, it is explains this in more detail, and how and why an el-natural tank works.