Urgent help + rep plzzz! Empty reservior? Nft

When should i change my reservior? i havevn't done anything to it in 5 days, my m8 said i need to change it and add new nutes every 2 days, this is a hard job, as it is a 50 litre reservior, i have no cf meter to measure how much nutes are left, what should i do, plz help ahhhhhh

You should be good for 3 weeks with good nutes. If I could I would change my rez every other week. Follow the instruction on the bottle should be good enough without using a TDS meter. But it will be hard to dial a strain in for how much nutes it can take.

Your 50L tubs are a little over 13 gallons,my tubs are 8 gallon and they are around half full.I empty them every two weeks and refill to the halfway mark everyday,use half strength nutes to refill everyday.OPH

mine is half full, you reckon topping it up with 5litres of nuted water a day and change every week should do it?

I would not fill the res up all the way,the roots like the oxygen.Only the bottom 1/4 of the roots need to be in water.
If your res is half full and your roots are in the water,just keep it half full.
When i start a grow i fill the res to the pots to keep the roots moist.As the plants and roots grow i drop the water level to half of what the res holds.Like i said the plants realy the oxygen.
Just mix up some nutes at half strength to keep your res at half full.
When and how often you change your nutes is up to you.I change mine every two weeks unless something is wrong and my plants are not doing well.OPH