Copepods are absolutely a must for all mixed-reef aquariums. It would be best to get a set that comes with the three major benthic (surface-dwelling) species, Apocyclops, Tigriopis and Tisbee.
However they alone are not going to solve this issue. My tank is new, and having a heck of a diatom outbreak in the fuge. I've also got pods swarming everywhere, but they're just not enough. I'm waiting on more CUC to clear observation before I put them in, they would no doubt help a lot, but even they I do not think would be enough - not at this stage in the tank's life-cycle. Early diatom blooms are just kind of a fact of life in any aquarium with lights and silica in the water.
I've actually got a 50% water-change planned for tonight/tomorrow (primarily because nitrates are high), and while I usually don't siphon the gravel directly, I'll be doing so in the fuge to remove the excess diatoms that I've blown off the rock or scraped off the glass and have settled on the bottom... R.I.P. to all the poor pods that are going to get sucked up in the process, but it has to get done, since removing the diatoms themselves will also export the silicates they've taken up.
Thankfully, said refugium is paying the bills and doing all the heavy lifting. Despite some remnants of the diatoms making their way from the fuge into the DT when I clean it, the DT is almost entirely free from them (PAR and photoperiod is also MUCH higher in the fuge than in the DT).
Still, simple export is the best way, especially if it's just a reasonably new tank (as it looks to be... less than a year old?), and getting some macro algae growing (or a turf scrubber) going in your sump will help in the long-term.
While Phosguard is also an option, if the tank is actually more mature, you'll want to find out why your silicates are high enough that diatoms are running away - are you using tap water? Do you need to change RODI filter media? Could it be your salt mix?