Ok heres what i found about NitraSafe:
INTERPET NITRASAFE
Nitrate is an end product of the breakdown of toxic waste and is therefore present in most aquariums. It directly affects fish health (causing stress and weakening them) and causes algae problems. In some areas, nitrate levels in tap water are becoming increasingly high, so changing the aquarium water is no longer a safe method of reducing nitrate. The levels of nitrate in your aquarium should be regularly monitored using the Interpet Easy Test for Nitrate. Levels of nitrate over 50mg per litre are undesirable and should be reduced using Nitrasafe. Nitrasafe can be used safely in freshwater aquariums or to pre-treat water change water. Easy to use nitrate removal sachet can be placed directly into the aquarium or in the filter. Fast and effective, removing up to 7,000 mg of nitrate to a safe 25 mg per litre, in a few hours. Reliable and economical - Nitrasafe cannot 'dump' removed nitrate back into the aquarium and the
sachet is rechargeable with a simple salt solutionot suitable for use in marine aquariums, but can be used to pre-treat the water
Price: £11.50
It cost £11.50

So i have to keep doing the water changes for 3 weeks