Putting ice -freeze bottle is way too troublesome. Need a good chiller to improve the water condition in marine tank.
2nd hand skimmer is ok, provided there is no crack, pumps working normally etc. I got myself a 2nd hand H&S skimmer more than 1.5 years ago and still luving it. Every 3 days need to clean the collection cup. IMO, invest in good skimmer in any marine setup. Or you can do the algae scrubber way...