Well, at game start the tax rate was at 34%, I believe, and I did not touch it until I notice the dramatical drop of approval. So I lowered it first by 2-3 %, and afterwards, since this had only a short term effect, again to below 30 %. I believe it was at 28 % when I gave up the game. What I found odd too, was the extreme population growth. The game starts with your homeplanet having 5 M citizens, after only 36 turns (3 auto savings, that's why I recall this) the population size had more than doubled. Since this are week turns, such rate seems a bit extreme. But other than by tax rate, social improvements and propaganda the manual does not say anything about issues, like overpopulation, causing drops in appproval.
Is there a way to control population growth?
By the way, the custom civilization I defined had an advanced loyalty bonus.
So you see, I was at the very beginning of the game, apart from my homeplanet I had gained one more colony only.

More population = less morale. Each colony produces a base of 3mt/wk which allows 3billion people to live on a colony at 100% morale.

I saw a tip posted by somebody (maybe popup) which basically went along the lines that you should never build food producing improvements until you have the technology to keep an increased population happy. If your goal is to have a high morale then this strategy certainly works.

On a technical note I would be interested to find out precisely how morale is calculated.

To keep the population happy (above 50%) on my home planets I've had to build 3 zero gravity stadiums and the political capitol. Morale resources help some, but they (and all the other resources and econ starbases) have been nerfed compared to earlier betas.

Has anybody used the extra funds area in the planet detailed screen yet to see if this helps... personally I have had my tax rate down to as low as 25% and was barely in thegreen with morale.

Two things that some people may not realize that affect this. First, a low morale does affect population. Try it, if you raise your taxes far enough, the population on your home world will actually drop I find I have less of a morale problem if I never let my tax rate go below 49% until later in the game. Set it too low, and your home world population goes up instead of down, and then you wind up with worse morale problems.

Second, the PQ of a colony also caps the population. So, we wind up with three possible limits. PQ, food, and morale.

On a PQ 4 or 5 planet, the PQ limit will be the limiting factor, if I remember correctly, so a farm is a waste. A PQ6 planet can have a population of 3.5B max, so it's only gaining 0.5B from the farm. That's a bit more tax revenue than you'll get from one improvement, so sometimes I'll use a farm there.

PQ 10 and higher have population limits high enough that morale can be a real issue. Even 9 can be bad at times. Because of this, I never put a farm on anything PQ10 or higher, and don't put one on a PQ9 planet unless i'm willing to dedicate 2 or three tiles to morale.

Agreed, Lucky Jack, it's just that the population on a planet with a PQ higher than 9 can get out of control, which is why I use the 6-9 planets as my revenue base. In my current game, I can only spend 2/3 of what I'm making, so it can't be too bad

If you put your mouse cursor over the approval rating it will pop up with what is causing it.

If you put your mouse cursor over the approval rating it will pop up with what is causing it.

It tells us what is causing it, but those things vary to such a degree as to make that information feel almost useless. For instance: in my last game, on my home planet, with 10.72 b, and a tax rate of 68%, I had -158 from taxes. The next turn, I had -85 from taxes. then back up. With no changes to tax rate, no changes to spending. I wasn't at war, etc. It's all very weird. I've had planets go from 60% down to 30% in one turn, and vice versa (same planet, a few turns later), with the only thing that I did was open the detail view of the planet.

From what I've seen in my past few games, it's almost like opening the planet causes it to recompute the morale. So I've gotten to the point where once it seems to stabilize, I leave that planet alone for as long as I can.