Check the listing for details. pH 4.01 & 7.0 Calibration 100 Tablets Makes 64 oz / 2Quart hydroponics buffer. Condition: New. Listed at 32.48 USD. pH 4.0 & 7.0 Calibration Solutions 50 Tablets Makes 32 oz / 2 Quarts of hydroponics buffer. This listing is for 50 tablets of EACH pH buffers (100 total tablets). Each buffer tablet makes 20 mL of buffer solution, so these 100 tablets makes 2L of solution, which is a little over 2 Quarts total. Use the pH 4.0 & 7.0 Calibration Solution is used to calibrate your pH meter. Easy to use, just dip your electrode into a small amount of the buffer and adjust the meter to read 4.0/7.0. Suitable for all makes and models of pH pens and meters and all general hydroponics applications. This standard reference solutions is of the highest quality and allows growers to calibrate many popular meter brands with confidence (NaCl scale or the 442 scale). Each batch is carefully checked to ensure that it is precisely calibrated and yields reliable readings every time. Grower’s Tip: When getting started, it’s a good idea to measure the pH of your water everyday, until you get a feel for it. Measure your water and then add the nutrients. Within an hour check the pH and adjust accordingly. Repeat this process until pH stabilizes. After several runs you can generally get a feel for how much to use. Keywords: HANNA Milwaukee HI70300 MA9015 HI70004 MA9004 HI70004 M10004 HI70007 MA9007 HI70007 M10007 HI7010 MA9010 HI70010 M10010 GH47 General Hydroponics