my filtration is fx5 and a rena star xp3. I also have two aquaclear 110 that I am not using and contemplating putting on the tank. I do weekly water changes and my nitrates are always under 20 ppm. My nitrates are low.
I kept 3 retics in a 125 for nearly 3 years with no issues I had awesome filtration and was religious on water changes. Retics still get big though as I have a female that is nearly 15 inches in disc size.....
for example, i have 2 retics at 8 and 9 inches in disc, in a 300 gal with a 90 gal sump, using a wet/dry trickle tower filled with approx 200 pot scrubbies and bioballs, more pot scrubbies in the sump itself, as well as a sponge filter, and then i have a fluval 405 filled with ceramic rings, and even then, i'm doing water changes at least every other week.
overdoing your filtration is preferred to underdoing it.