I also have a reefer 170 and think the biggest limitation is space as the cabinet is pretty tight. Both options you mentioned will reduce nutrients but take up a lot of space.
How high are your nutrients?
If they are very high you might want to try carbon dosing as that seems to be the strongest reduction process in my experience. My go to would a big dose of biodigest to promote good bacteria growth and dosages of potato vodka.
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If your nutrients are only a little high maybe just add a ball of cheto and a cheap par38 light in your sump. Its a pretty cheap but effective option.
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If you want a cleaner look in your sump Santa monica makes a mini turf scrubber that would fit in your sump. (I have never used a santa monica product but they looked like a good option when I planed out my 170 build)
https://www.santa-monica.cc/SLIP7-nano-chaeto-reactor-waterfall-scrubber-upflow-scrubber_p_104.html