Controlling temp and algae in EZ-cloner 60

I am a new EZ-clone user (two weeks old) and am trying to root juniper and other cuttings in the machine. I apologize for being a little off-topic, but it seems that only Cannabis hobbyists have the skills and experience in doing this.

Because they're junipers and other woody cuttings, they need to be in the propagator for about six weeks--plenty of time to develop problems. The temperature of my basement is 68 degrees; however the tub reached 80 within a few days. The water is currently at 78 degrees and a slimish/furry white growth is forming on the surfaces.

I used tap water, took the pH to 5.2, and added Dyna Gro ProTek and KLN at the start two weeks ago.

Any tips on controlling the algae now? Should I try changing out the water and disinfecting the tank and pump?

Should I try adding a chiller to the system? When I do a search for chillers I find tips to add a chiller but no detail on where I would run intakes and whether or not I could put it in series with the existing pump.

I've read that some people freeze water in plastic freezer containers/plastic cubes and use that for temperature control, but that seems rather interaction intensive and might introduce additional contamination when used over the course of weeks.

Any help is very much appreciated!