The item you are inquiring about i an Adjustable Recycling Timer which certain models include a photocell for day / night timing modes most which allow adjustment of the duty length of the powered on cycle and adjustment of duty cycle powered off periods before the cycle resets and repeats.
The model i have is discontinued, the CAP ART-DNe Adjustable Recycling Timer
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Elevated Lighting Company has this item available
Autopilot Advanced 24hr Recycling Timer
You can inquire with your local municipal water supplier for specific water quality information.
Nutrient burn is common enough among growers whenever light, heat, humidity and water quality conditions are altered as the plants usually lower their nutrient uptake and usage resulting in excessively high chemical fertilizer levels the plant is unable to moderate the effects from. The majority of plants with the exception of succulents have adapted to their originating environments without the ability to store large amounts of moisture reserves and and must constantly pump a water supply from their root systems to maintain cellular rigidity and function. Most plants can not simply say No' to whichever water supply they have access to if the supply increases in brackish salinity or turbidity.
The last photographs of your plants damaged leaves I am capable of seeing phosphorous and calcium deficiency with small amounts of either nutrient burn or too great total PPM nutrient solution strength exposure. Nutrient burn is first evident at the growing leaf tips as damage tips. Larger leaves which become hard, curl and die are caused by excessive high PPM nutrient exposure.
I suspected that your nutrient solution ppm were high, making it difficult for your plants to properly absorb the nutrients, water in ratio and your plants are currently using more water than nutrient in solution. I advise you lower your nutrient solution by adding 25% more ph adjusted water to the nutrient solution you are currently using.
During daylight exposure plants use photosynthesis and are in turn able to process nutrients, during night time plants absorb more water from nutrient mixtures increasing the ppm strength of the nutrient mixture. Plants may also leach back metabolites and excess nutrients back into the nutrient solution all resulting in altered pH with higher concentrations of unused elements in nutrient mixture imbalances necessitating the reservoir cleaning and replacement of the nutrient mixture.
Short term solutions are mixing either distilled or reverse osmosis water into your available water to lower the total PPM to acceptable ranges.
long term solutions are use of a water filter that is able to lower dissolved solids from your water supply or use of a reverse osmosis water filter and reservoir to supply your water requirements.