Come to think of it approval was going down as population was rising...   Thanks!

Glad to help, and glad to see that the game is still getting new players.

First of all, calm down again. You are freaking out for no good reason again.

Now here is the deal:

There are two sources of unhappiness:

1.) Population getting to high (overpopulation of a planet). and

2.) Too high of a tax.

There are many ways to boast happiness:

1.) Morale Buildings.

2.) Morale ability of your civilization.

3.) Special events from the United Planets

4.) Random events from planets.

And others.

To deal with unhappiness here is my suggestion:

You should not attempt to deal with the overcrowding problem. That is normal and expected. Only reduce taxes if it is above 33%.

Morale Buildings and your morale ability should be your primary weapons to combat this problem. You are Thalans, so you should bet powerful techs and buildings that gives out morale. If possible, also trade with others to gain morale techs to stack up with your own. Harvest as many morale resources as possible, and take advantage of the random events that comes along. Also, try to obtain as much morale boosting trade goods as possible.

As for the "planet ain't being used at its max potiential", it is just a stock complaint that does not have too much meaning other to give the game its character.

Approval is not hard to master I tend to stuff my races with happy bonuses and trade for morale buildings anyway.  I play at 80% tax with near 100% approval across the board.

TA's morale/approval isn't more than marginally tougher than DA's (DL is somewhat different matter)-provided you stick with the Terran or Minor Race tree.

Using other trees means you don't get all the morale trade goods, nor various bonuses from techs, but the extra mining modules that a number of trees have more than makes up for this loss (in late game), provided you have sufficient morale resources.  Granted, the early game is tougher.

Bottom line, you can still run 79% tax and 20%+ approval on 20B pop colonies with maxed out morale, or alternatively 39% tax and 100% approval at 20B pop.

In order to run 100% approval at 79% tax, with the above 20B pop planets, one would need about 80% approval from buildings, since your native/racial morale is capped at 100% after depreciation by population, and since at 20B pop you only get about 1/3 of the value, this means your raw value needs to be about 240%, which requires 6 VRCs.

Frankly, that's not something I would consider worthwhile-stock markets would be better, of course-but it can be done.