Been lurking on here for last two years keeping my pool in check with all the knowledge in these threads but I can't figure this one out. Have a 24' 48" high above ground liner pool with a sand filter and intex swg which works great. Pools clear and clean. Problem is my ph read low on the quick test so I dumped in a bag of baking soda. Stil read below chart after a week so I took sample to my work with a proper pH meter and ph is below 4. What causes this and what's the best way to remedy it. Seems like a lot of baking soda to fix. Is a dump and refill in order? Thanks for any help.