Fish In After Cycle And Low GH And KH

Hi and welcome    I don't think we have any other members in Norway!

Well done on the fishless cycle. I too had a pH crash during one due to low KH so I know what it's like - went from 7.5 to off the bottom of the scale (ie below 6.0)

As you are aware, you can't use baking soda with fish because of the sodium content. I have heard of dolomite or aragonite being used to harden water, either chips or sand. I think those who have Rift lake cichlids use it as those fish need very hard water.

As for your holiday, there is a conflict. The idea of fishless cycling is that you grow enough bacteria for a tankful of fish so it seems wasteful to get only a few. But if you got a tankful just before going away, you won't be able to keep an eye on it.

There is one option, but you may not like it. Dose up the tank with baking soda, add a 3ppm dose of ammonia and wait till you get back to buy fish. If someone would go in every 3 days and add the amount of ammonia you tell them for 1ppm ammonia, that would keep the tank cycled till you get back. If there is no-one to dose it, you'd just need to make sure the bacteria were OK by adding 3ppm ammonia on your return, though they might have gone dormant and you'd have to wait till they woke up again before getting fish. This is why I say you might not like this option 
There is another advantage to doing it this way. It is not unknown for new fish to die. Some of them will be weakened by the treatment that have received since being shipped from the fish farms. I would be very wary about getting new fish just before a holiday because if one were to die the day after you left, that's 9 days for the body to decompose and foul the water. You could be lucky and have all of them survive, but I wouldn't risk it.

Thanks for the comments everyone.  Main reason I didn't want to go with a full stocking of fish was I thought you were not supposed to but rather introduce groups say once a week.  The tank is for my children (now my hobby) and I wanted to do a fishless to teach them how to do it, how to wait and try to be a bit more ethical.

So we have a thriving planted tank with a fair few snails at the moment. Final stocking will be mixed rainbow fish, platys, chain loach if I can get one, cardinal and black phantom tetras, and maybe some raspboras or danios.

Went to the LFS tonight but the main fish expert was not there.  I picked up some products that are designed for Norwegian water as it seems the low GH and KH are a big problem. They are NORAQ and the GH-Salt and pH\KH+ in theory they wont dump as much sodium (or any?) as the baking soda route and can be used fish in. I will talk to my LFG later this week.

So plan is to dose to keep KH and GH up and then dose with ammonia before we leave. hopefully I can get someone to come in a couple of time a dose the ammonia again. After we get back I will try more natural remedies, such as crushed coral and dolomite.
 
I also bought an automatic feeder for the Rio. Does anyone think that using the fish flakes as source ammonia would keep the bateria going and I wouldnt need to dose ammonia? I started the cycle that way and it got going before I could find a source of ammonia in Norway.  It worked but was pretty temperamental.