Hey man, as @wildeweed said you will constantly battle with pH and issues with your plants unless you get some nutrients that have good buffering capability. General hydroponics maxigro and maxibloom are the answer to your issues. It's cheap and it will hold your pH steady. The situation you are in now having to knock your pH back down all the time is stressful for the plants. The roots don't like constant fluctuation up and down. You can rotate frozen water bottles to keep it cool, but that won't actually change your pH. pH readings increase as temps drop but it is still technically the same. Just give the maxi nutrients a shot and it will make your life a lot easier.
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