filtering a 125

hello..

Question for you guys...I have a sunsun 304b and a eheim ecco 2236 filtering this tank but after only a week my fish feels a bit sluggish but when I check my water its good. Any reason why they are like that? Is
it a lack of filtration or am I doing something wrong? I also have purigen in the filter as well. Any info appreciated! Thanks!

ammonia 0 nitrite 0 nitrate 5 ph 7.6

But after a 50% wc they are fine now..

Thanks! I'll give that a try. There is some agitation but there is a light oil film on top if that makes a difference.