It's the temperatures and light intensity as well as duration of light that need to be monitored.
Remember seeds are looking for moisture and warmth some look for light they don't need fertiliser until after the first true leaves appear usually after at least a week or 2 after germination
Don't use tap water in London it's too hard for most plants
And they add chloramin(made from pee) which doesn't evaporate and will buildup in the soil leading to future problems that will be misdiagnosed on this site.
I only use bottled water that is at a PH level of 6.2 and 70 parts per million in the water.
I started using a TDS meter to measure the parts per million
And a PH meter but not ant more as bottles water is quite reliable when it comes to the ph and ppm
I only fertilise the plants rarely to give the soil microbes a chance to establish them selves.
I grow thyme, lavender, strawberries, mint, cilantro, parsley, basil, spring onions, garlic ....
All indoors inside window box with the aid of an LED system that is dimmed down to minimum at 46w !
Notice how the strawberries and some of the mints prefer the sunlight over the LED radiation I think it's due to the intensity I will experiment when the plants are bigger