20kg Blue Horizon TA+ Raiser. This swimming pool TA increaser for pools, hot tubs swimming pools and spas will help you to balance (by raising) the TA in your pool water. Granular formula dissolves quickly to increase total alkalinity. Castle Hot Tubs is a well-established, trusted name in the water care industry, we will do our very best to ensure that your purchasing experience with us is a pleasant one. Goods ordered before 1pm will be sent out on the same day.