Define economical... better to let us know your budget.
In any case, 25 degrees for a 1.5ft tank, a small aquarium chiller would likely be way to go.
For that temp, fans are pretty much out of the picture. A few ppl can get 26 degrees, and that is usually around the cooler months of the year. The average is 27 or higher.
For pH testers, you have the chemical test kits (about $14?) or the test pen ($60++ to $100++). Test pens are much more convenient.
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