If you have marine tank using the 'berlin' filtration standard then you do need a protein skimmer. However you would not need a powerful external filter with biological media in it. Other marine filtration methods vary as to the requirement of a protein skimmer.
If you have a freshwater system you generally don't need a protein skimmer.
I think you're probably just seeing the effects of water losing some of its gasses. as you know if you leave a glass of water on the side overnight in the morning it's got bubbles stuck to the glass all the way round. These little bubbles form everywhere but are redissolved and/or escape through the water surface over time so you never normally notice them. In a normal tank that bubble forming under the bogwood would eventually just bob to the surface and be gone. Then a new one would slowly build up. With the closed top design of the edge it just makes the process more obvious.
Keep your eyes open for the problems Cathie and Suey described but I think you'll find that the only fix would be to ensure that the top slopes towards the opening so the bubble can escape when it forms.
Re: anyone else laugh when that lady put the cat in the bin?
ah but did that one come with a you-tube video and national tabloid coverage? Many people don't realise what's going on all around them because the media don't or can't report it. I think this is why they get so shocked when they hear a pensioner is mugged a young girl kidnapped or a pet mistreated. I think if most people had a clear understanding of what goes on in this world they'd lock the doors, black out the windows and sit under the kitchen table shivering!
As Cathie says, you need a TDS meter to ensure that the water after filtration is pure. You need this whether you make your own or buy it. A pen type TDS meter is cheap from ebay and you just dip it in the water to see how pure it is.
The GPD (gallons per day) rating on an RO unit is under ideal conditions, which means that the water is warmer and under more pressure than it's likely to be in real life. You can half that to get a more realistic GPD figure. I have 100GPD unit, this results in about 2.5 hours to fill a 25L jerry can. I also have a 3 gallon tank though that holds about 15L under pressure so I can actually fill the first 25L can in about 25 minutes. One with a pressure gauge is good as this is an excellent diagnostics tool.
If you're making your own you also need to consider the costs of replacement filters and possibly DI resin. Not too expensive but needs to be done every 6 months.
It will only work if the bulb has the right lighting for coral photosynthesis. This is not quite the same as terrestrial photosynthesis, it's more blue because the blue light penetrates the ocean better. Generally if a bulb does not say it's designed for corals then it won't work very well at all.
You also got salt creep to worry about, the link you gave is broken but if the MH unit is mild steel or any other normal metal then the risk of corrosion and electrical shorting is very high. If it's not water proof then there is also a significant risk or electrocution as salt-water makes an excellent conductor and the constant evaporation from a marine tank will contain just enough salt to get into all the electronics. (Although we say only the water evaporates a small amount of salts are dragged up with it and are deposited on the first cold object they find. Over time builds up.)
Probably not the answer you hoped for but I hope it's helpful none the less.