Or if the tank is heavily planted do a silent/plant cycle as squidneh said.
If you have a lot of plants in the tank (looks like maybe you do?) you can do a silent cycle. The plants will take nutrients (like ammonia) out of the water column which will keep your water safe for fish. Using this method you just plant your tank heavily with fast growing plants - floating plants are the best for keeping water clean - and once they are healthy and growing, you can add in your first group of fish.
A silent cycle removes the need to actively cycle your tank. The people who said to use fish food to cycle the tank mean well, but if you want to actively cycle the tank you would want to use ammonia drops, not fish food, as it's more accurate. But it isn't recommended to use both plants AND add ammonia to cycle - pick either actively cycling or simply adding enough plants to maintain water quality.
ETA: bacterial blooms are common in new set ups. I'm guessing that's what's going on in your tank. Usually they resolve themselves within a few days.
The white stuff in the tank water is likely to be a bacterial bloom.
Perfectly normal during the cycling process and will go away on its own accord during the cycle when the bacteria and tank settles.
But please do not add any chemicals other than dechlorinater / tap safe and the right amount of ammonia for the cycling process.
And please do not add food as a source of ammonia. This is a very ineffective way of adding ammonia, and there are bad side effects of adding food when there’s no livestock to eat it is planeria worms or bad water parameters. Simply not worth it.
Not sure if you’ve already read this or not but certainly worth reading and studying if you haven’t.
By chemicals you mean to adjust the ph? But fertiliser is OK?
Cycling Your New Fresh Water Tank: Read This First!
Cycling Your First Fresh Water Tank What is Cycling and Why is it Important? Fish waste, and especially fish breathing, plus uneaten food and other organic matter breaking down in a tank all produce Ammonia. This can quickly become toxic to fish if it is allowed to build up to any measurable...www.fishforums.net
Wow I don't know if I'm more or less confused lol have read about planted fishless cycling adding ammonia, not adding it, adding fish food, not adding it, one person mentioned adding urine (???) but thanks everyone for your input and efforts.... Hopefully it is a harmless normal bacteria bloom. If none of you recognise it as something terrible then that's reassuring at least.
Thank you for this... so really, I can just do the water changes and let the plants settle in (more plants are coming)... if they're all growing and healthy that will mean the system is working? Will that mean the levels on the tests always come up zero then, until fish are in there?
I am cycling my tiny tank again now too so that it can be like a quarantine area or sickbay, or maybe keep snails in it or something one day, but it just has fake decor - have been adding fish food, will that be OK for a 16l tank or really need to get actual ammonia?