The bubbles are out of the water. I presume you used a lot of cold tap water? The colder the water the more dissolved gases it can hold, and vice versa. So as the cold tap water warmed up a lot of the dissolved gases stopped being dissolved and formed the bubbles.
Are you going to plant lots of live plants and use them to take up the ammonia made by the fish, or do you plan on having mainly fake plants?
Testing the water won't show if it is ready for fish because with no fish there is nothing to make the water 'bad'.
If you plan on fake plants you will need to cycle the tank before getting fish. The Stability may help but you can't rely on it to cycle a tank. It may or may not contain the right species of bacteria, and if it has ever been stored incorrectly (eg freezing or baking in a lorry) it probably won't work. It is worth getting some ammonia and adding enough of that to give a reading of 3 ppm, then test after 24 hours. If you then have readings for ammonia and/or nitrite above zero, you need to do a fishless cycle.
https://forums.thinkfish.co.uk/fishtank-filtration-and-cycling/fishless-cycling-how-to-do-it/A 170 litre tank won't hold 170 litres water because most manufacturers include the thickness of the glass and the air space above the water in their quoted volume. I would assume 150 litres. Most ammonia is 9.5% so you would need 4.75 ml ammonia to get 3 ppm. A medicine dosing syringe is ideal for measuring small amounts.
However, if you intend having a lot of live plants, particularly floating plants, they use ammonia as fertiliser. Plant the tank and wait a week or so to make sure they are thriving, then add fish a few at a time, monitoring ammonia and nitrite every day. If you see a reading for either above zero, you'll need to do water changes to get them to zero, and hold off getting any more fish for a while.
You are aware that danios need cooler water than most fish? This will restrict your choice of other fish to those that also need cooler water.
http://www.seriouslyfish.com/species/danio-rerio/ We should aim to keep the temp in the middle of the fish's range. In the case of danios this is 22 to 23
oC
Danios are fine in hard water, but lots of other fish do not like hard water. Always research fish before buying -
Seriously Fish is just about the best site for research.
On the subject of hardness, it would be very helpful if you know just how hard your water is.
If your water company is Wessex water, just type your postcode in here
http://www.wessexwater.co.uk/waterquality/ If you are with Bournemouth Water, this is the page
https://secure.bournemouthwater.co.uk/postcodesearch/household.aspxYou need the number and the unit as there are half a dozen units they could use and you may need to convert it into one of the two units used in fishkeeping.