Coming from years of hot tub ownership I figured pool chemistry would be similar, but the volumes involved are throwing me off. My spa holds about 400 gallons so I dose everything by the ounce, but now I'm staring at 18,000 gallons and trying to figure out how to scale that up without just dumping in a ton of product and hoping for the best. I tested the water this morning and my pH is sitting around 7.0 and I can't even get a chlorine reading yet. Is there a good starting sequence people follow when you're bringing a pool up from zero, or do you just shock first and then balance everything after?
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First time opening a pool, hot tub guy here - totally lost on chemicals
- Thread starter soaklife
- Start date
The math isn't as scary as it looks, I promise. Your pool is essentially 45 times the size of your spa, so if a product calls for 2 oz per 400 gallons you'd need about 90 oz for your pool. That said, most pool chemicals come with dosing charts right on the label based on pool volume, so you're usually better off working from those than trying to scale up from spa doses manually. The measurement units shift too - where you were measuring in ounces for the spa, you're now measuring pounds and sometimes gallons.
One thing that tripped me up my first season was assuming I could make big corrections in one shot the way you can in a small spa. With 18,000 gallons you really want to dose in steps, retest after a few hours of circulation, then adjust again. Overshooting pH or alkalinity in a pool is a pain to walk back. If you let us know what your pH is actually sitting at and what your alkalinity looks like, people here can give you something more specific to work with. What test kit are you using? That matters more than most people realize when you're just starting out.
One thing that tripped me up my first season was assuming I could make big corrections in one shot the way you can in a small spa. With 18,000 gallons you really want to dose in steps, retest after a few hours of circulation, then adjust again. Overshooting pH or alkalinity in a pool is a pain to walk back. If you let us know what your pH is actually sitting at and what your alkalinity looks like, people here can give you something more specific to work with. What test kit are you using? That matters more than most people realize when you're just starting out.
Yeah the pH thing is actually pretty common when you first fill or open a pool. Fresh water, especially if it came from a hose, tends to run high. You dont necessarily need to slam it with a huge dose of muriatic acid right away - add maybe a quart, let the pump run for a few hours, then test again. Chasing pH in big jumps usually ends up with you overshooting in the other direction and then you're correcting the correction all day.
The one thing I'd say coming from hot tub experience is to stop thinking in ounces pretty quickly. At 18,000 gallons you're working in pounds for most dry chemicals and in cups or quarts for liquids. The mental shift takes a week or two but it clicks eventually.
The one thing I'd say coming from hot tub experience is to stop thinking in ounces pretty quickly. At 18,000 gallons you're working in pounds for most dry chemicals and in cups or quarts for liquids. The mental shift takes a week or two but it clicks eventually.
The label dosing charts are your friend here, but one thing to add - at 18,000 gallons with a pH of 8.2, you're probably looking at around 32 oz of muriatic acid to bring it down to roughly 7.4, assuming average alkalinity. Test your TA first though, because high alkalinity is usually what's keeping pH stubbornly elevated, and you'll want to address that before you keep fighting the same battle every week.