my biggest fish is my blenny who is around 7-8cm and my next biggest is my yellow watchman who is a little smaller than that most of my fish aren't that big yet since my oldest fish are my clowns who are I have had for 9 months and they were around 3-4 cm when I got them they are like 4-5cm nowThose are all small fish, correct? Less than 3-4”?
my 125 has
2 chromis
1 kole tang (full grown, pushing 8”)
3 wrasse
1 orange shoulder tang
Falco hawkfiah
Mandarin
Midas blenny
2 clownfish
and with those 12 fish, my nitrates stay between 10-30 and phosphates 0.02-0.1 depending on feeding, filter sock cleanliness, and how much I run skimmer.
I find it is easier to fight high nitrates than it is to fight low nitrates, but opposite for phosphates. In the first year just test test test and that way u develop good baseline and what is “stable” for your setup, then try to keep it as close to that, as long as everything is happy and showing growth