"A few" midevils in a 180g is going to cause the same nitrates as 1 in a 90g no?
Op, if it's a female rd she will be fine forever in that tank imo, most store bought fish end up much worse. If it's a boy I agree in 2-3 years he may start looking cramped and think the 180g would be a great step up for him.
My 300g has the equivalent body mass in fish of about 6 fully grown midevil males (if not more) and I control my nitrates with spares feeding and 1 80% WC per week. My tap water is 30ppm and I get a reading of 50ppm at the end of the week.
I understand completely where duanes is coming from tho bigger is always better as is less nitrates. Most accept that 4* length and 1.5* width of the fish is a bare minimum.
You will get lots of various opinions on here and alot of very conservative opinions depending on what side of the bed people climbed out of.
@eh for example has had his midevil in a 75g for a few years now and although not ideal he seems to be doing pretty well. I bet all his siblings have had tragic lives in 3ft tanks with no water changes. That little devil should thank his lucky stars he ended up in an mfk'ers tank