If you have a tank full of acropora then you want to treat them with medication. Red bugs will not kill acropora but will slowly weaken them over time an reduce polyp extension. Ultimately, this may result in the death of the coral or cause RTN if it gets bad enough.
Dosing interceptor is the best and lowest risk treatment. There are literally no negative side affects aside from potentially killing shrimp and crabs. Lowering your tank temp and potentially killing everything is very risky. Adding another animal to kill the red bugs is a waste of time and you'll just end up killing the pipe fish.
Spend $60 on the meds and wipe out the red bugs swiftly.
If you choose to go the dosing route:
Go to joespetmeds.com and order large dog interceptor spectrum. You must to administer the treatment three times over the course of a month or so. If you do not dose three times the red bugs will come back.
Remove the crabs from your tank or risk keeping them in. They might be dizzy or lethargic for a few days, I once dosed with my blood shrimp in the tank with no issues. I added a whole pill to my 150g reef but some people use less. I didn't bother running carbon afterwords and didn't do a water change. I didn't have any problems, you can do both if your concerned but let the meds run for 24 hours.
I for one wouldn't be able to sleep at night knowing my babies had fleas irritating them. Just one man's opinion however.
I would get rid of them.
Like Joe says, you can grow and colour up SPS with Redbugs in your system...BUT I say get rid of them for a few reasons. I had Redbugs in my system around a couple of years ago. They were in my system for at least 8 months. I did notice their population go crazy and then reduce...not sure why.
During the time they were in my system some SPS wouldnt colour up:
SSC and some smooth skinned. The SSC was nicely coloured up before the RB's. Tenuis and Selago etc lost their green base and became brown.
Other SPS lost PE:
SSC and Granulosa and a few others lost PE.
Millepora etc were not affected as far as I could tell. These were still nicely coloured and had great PE.
After I treated for RB's I remember how the granulosa quickly regained PE and the SSC regained PE and colour. Actually, the SSC looked pretty unhealthy...within a week of treatment the SSC looked so much better!
I used to think they are not so bad before. I remember a thread from around 12 years back reefers were arguing over whether RB's are really bad or not. Back then and upto the point before I treated my tank, I thought they arent so bad...and they arent...but they do impact some SPS more than others.
However I would treat my tank right away now if I found my corals were infected with RB's.
All my SPS get a 10 hour triple dose of Interceptor and QT before going in my system now.
For sure ones corals can survive just fine with RB's in the system, but IME not all will be at their best. i didnt lose anything, but have heard of others losing some acros to RB's due to over infestation.
The other thing to realise is that you cannot swap/sell frags...even selling a zoa on a frag plug can potentially infect someone else's system. Not saying you personally, but just pointing out the potential impact.