hi lads a have a commercial unit to wash  and it has storage tank outside , with liquid nitrogen in it would a SH mix at say 10 ltr 2 gallon to 200 ltrs water 50 gallon be to strong a mix  for it or should i use a weaker mix on it and does it react in anyway with the fitting or pipe work on these cylinders ???

got job booked for Monday morning the unit is not that bad dirt wise its the mono blocks that's surrounds it. Washing and sanding it back up and they want it sealed also any advice on a good weed killer or weed inhibitor and a sealer that would cover 200 mtr  600 sq/f of mono blocks.

any and all advice greatly appreciated 

Thanks