My fish have attacked my plants and have made a right mess of the tank. I'm going to have to do a large water change, some where around a 50/50 water change. I don't want to shock the fish with a large amount of tap water so i was wondering how long it takes for 40 ltrs of tap water to be save for fish.
Thanks.

You should be treating all tap water that you add to your tank with a water conditioner that neutralises the chlorine based chemicals - I use Nutrafin Aqua+plus. I also use a mixture of cold and hot water to bring it to the correct temperature. If you do this then you should be OK even changing half the tank.
Alternatively couldn't you net out most of the debris or syphon the water out via some sort of sieve/net and return the water to the tank .
If you can remove most of it then the filter should take care of the rest .

Buy a water conditioner from the aquarium shop. It makes tap water safe immediately. As the above poster said, you should be using this for every water change!!! For your plant problem you could use plastic plants instead. Real plants aren't necessary so long as you have enough aeration. I hav e just plastic ones.

Leaving water out to sit to remove the chlorine is quite an outdated method
it isn't really effective these days as it was a few years back as they add different chemicals to the water when it is treated now, so no length of time will make the water "safe"

using a conditioning chemical will however, make the water safe to be added to the tank straight away.

i use Tetra Aquasafe for mine, and try to match the temperature as closely as possible, using boiled water from the kettle and cold water from the tap
the temperature doesn't have to be perfect, just within a few degrees.

i understand if you don't want to be using lots of different chemicals in your tank, i'm the same, a water conditioner is the only potion i'll use with mine as it is necessary

as far as I remember the stuff in tap water doesn't harm your fish so much as kill your filter bacteria, which is very bad for a tropical tank.

Thanks for the advice. I always use water treatment, but normally I only do a 20% water change.
So i'll just continue doing the same. But this time I'm getting rid of the stupid natural fibre plants that have caused the mess and getting real plants.

if you've done regular water changes up until this point then doing a larger change shouldn't cause any issues. so long as you don't harm the filter bacteria it's usually grand. (though i've done a 70% change after a month without doing any changes without issue as well)

have you had those "natural fern" things that Supa make?
bloody horrible things. biggest mistake i've ever made, buying those. they look nice, but a proper pain in the backside. did away with them years back, the slightest but of movement in the water & they break up.

the fish will likely still attack the live plants, you might be best off with "Grass like" plants, Vallis and Amazon swords, as i've found the other "stem" types don't last long (though maybe that's just my set up)
Elodea does really well in tropical tanks, but be prepared that the fish will knock them loose.

i've got an on-going snail problem, so given in completely though and bought some fake plants to put in there as well as the last few vallis i still have.
there aren't as many snails in there as there used to be, and i've fished out/crushed as many as i can see when i do a gravel vac & scraped out any eggs i can find
the last few i'm going to leave to grow in there (around half a dozen of the blighters.) they're only Ramshorns, but they can look nice in a tank, especially the red footed ones.
i even added them to my goldfish tank when i had it, the goldfish liked them too.
very much enjoyed sucking them out of the shells & eating them, i wasn't impressed, but if they were happy then...

Yes I dis get the Supa natural ferns and a right mess they have made, the water even looks green.
Im thinking of getting some snails and clams to try and help keep the tank a bit cleaner.

If algae is a problem it could be that the tank is getting too much light. If its situated near a window it will go green pretty quickly. Even leaving the fluorescent lighting on too long can cause algae blooms. Try putting the lights on for no more than 6-8 hours a day. Also, if you do have real plants they will grow like the clappers if you feed them and introduce a co2 system to your set up. You can get ones based on yeast and sugar which are pretty inexspensive. Good plant growth will also help limit algae and keep the water in the tank in good condition.

My tank is algae free the colour was from the fibres from the fibre plants. Got rid of them today got 2 plants to start with, i dont think they will last long as my angel fish seem to like the taste of them.