From the product description, check product page for current description, price and availability:
For long term health of your elctrode use pH storage solution. It is a mixture of Potassium Chloride, Postassium Hydrogen Phthalate, Silver Nitrate, and Sodium Hydroxide.
Volume: 230 ml
Limited Availability Wine Deal of the Week: As of this posting, this is marked down to $8.99 as a MoreWine Deal of the Week. Shipping is also free to addresses in the contiguous US with most $59 Orders. Quantities are limited. Check the Deal of the Week section – Here – to see if this is still available.