For a friend who is just starting out with the hobby

[mr.sam]

A friend of mine asked me a question i don't really know the answer so I'm going to leave it up to the pro's. Please help if u can.

 

[mr.sam]

a pic of his problem

 

[Old Scales]

Have him test his tap water after it sits out overnight and gasses off. See what he is working with at the start. Could he be overstocked? Does he dose nitrates for plants?
Lots of missing information to give you a better answer. OS.

 

[mr.sam]

the info I got from him

 

[mr.sam]

Somebody told him it's most likely his RO unit but I don't think so. I think his tank is cycling.

 

[azmodan]

A friend of mine asked me a question i don't really know the answer so I'm going to leave it up to the pro's. Please help if u can. View attachment 235420

As OS pointed out its impossible for us to say without more info. Can you ask him for more specifics? Is he dosing nitrates? How old is the tank? How often does he do PWCs and how much? Heavily planted? Heavily stocked?