I ' m in Texas , so keeping things cool is the issue for me most of the year , but same things applyI use plastic reels and tanks they seem to hold temp way better than stainlessI use distilled water if I ' m going to run a lot of film , I put one jug in the fridge for a couple hours . I ' ve also poured some distilled into a sandwich bag and frozen it I can crush it up and add distilled ice to my beaker . In the winter , I may pour some distilled into a big plastic pitcher and microwave it either way , I slowly mix the water with a thermometer in it and can get it just right if I go slow . I use a small sort of bucket maybe holds a half gallon as an ice water bath just tap water , the graduate sits in it till it ' s goodI prewash every BW film regardless of manufacturer ' s preference . I use a distilled prewash , and get it to 20 as well . Pre wash a couple minutes and the tankreelfilm get to temp . I ' ve run film with a thermometer in the spout goes to the bottom of the tank and it ' ll stay within one degree of 20 for 12 minutes longest dev time , I ' m generally in the 68 minute times . I ' m getting more into using dilution vs . time if I want a little meat to the lower mids liking that look more than 150 for everything . If you ' re really having trouble , you could get a bigger tank , like a 2 roll and just run one roll , but fill the tank . More mass of liquid more stable temp . And , you can reuse that dev if you use it fairly soon get it back to temp of course . If the dev was expecting 2 rolls and you just soup one , the dev isn ' t exhausted yet . I dunno about color processing , but I ' ve had no trouble with BW temps , and the water coming into our house is all over the place , from bathwater warm to ice cold , depending on the season . Just did a pretty exhaustive test of Rollei IR , and ran multiple strips of 36 frames so consistency was vital to not make that a waste of time ! You should be able to nail this .