Starters prefer temps between 72-80 degrees Fahrenheit, (22-30 C). If it’s colder, it’s sometimes difficult for them to rise. Yeast likes warmth. You can stick it in your oven with the light turned on to help warm it up, you just want to make sure it doesn’t go over 104 F (54 C) or the cultures will die. Sometimes people will invest in a warmer to keep the temp consistent if their home is always on the cool side. I’ve found a 1:1:.75 feeding ratio is better for cooler homes when maintaining an established starter.