waterdrop
Enthusiastic "Re-Beginner"
Yes, its generally a good approach to separate ones thinking about mineral content and pH in the tank during cycling from mineral content and pH in the tank after cycling is over and the tank is running normally.
The tap water gives some idea of the baselines the tank might be near once cycling is over but is not entirely the same as a running tank, so its good to be planning to watch the pH and mineral content for a period after you get fish (assuming one understands what its likely to be well enough to have made the stocking choices) which should hopefully give a more true idea of what it will be like for years to come.
What model of eheim filter is it? Most of the larger eheim external cannister filters run several trays of media and often one of those trays contains a gravel-like material called ehfi substrat (or a larger, rounder ehfi substrat pro) which is really a sintered glass ceramic gravel. What you could do in this case is buy a box of fresh ehfi substrat for the donor and then together you just be careful to not take more than 1/3 the volume of this substance in the mature filter and replace it with an equal amount of the fresh media. Your friend should never even see a blip in the performance of the filter.
~~waterdrop~~
The tap water gives some idea of the baselines the tank might be near once cycling is over but is not entirely the same as a running tank, so its good to be planning to watch the pH and mineral content for a period after you get fish (assuming one understands what its likely to be well enough to have made the stocking choices) which should hopefully give a more true idea of what it will be like for years to come.
What model of eheim filter is it? Most of the larger eheim external cannister filters run several trays of media and often one of those trays contains a gravel-like material called ehfi substrat (or a larger, rounder ehfi substrat pro) which is really a sintered glass ceramic gravel. What you could do in this case is buy a box of fresh ehfi substrat for the donor and then together you just be careful to not take more than 1/3 the volume of this substance in the mature filter and replace it with an equal amount of the fresh media. Your friend should never even see a blip in the performance of the filter.
~~waterdrop~~
/aqadvisor.com/, However I found it a little generous on the stocking quantity with a 60l tank and I found a lot of people saying "So and so will mix, its worked fine for me!" and then the advisor stating these fish will murder each other. Of course once the tank has started cycling and stocking it will be in sight I will start a list and of course ask for advise 
The road to my girlfriends is mighty bumpy and I've been told to claim it off the council but geeze... I think it was just wear and tear to be honest! I guess my car will be a bit safer to transport glass fish tanks if I end up moving in the next few months.