hey guys, checked my CH level last nite with my tf test kit, unless i did it wrong my CH was 750-800. i have noticed the tiles above my water line have gotten this white looking crust on them, and also i do get the tan-brown spots on the bottom of the pool that seem to come and go. i just recently purchased this house with the pool, so im fairly new to pool care, but i've learned alot here. all my other tests on the pool are coming back in the norm range, what has made my CH so high ? and how can i lower it back to the norm? (BBB method by the way) 20,000 gal gunite pool, approx 15 yrs old

Test the CH of your fill (tap) water. If it's high, then that is your source of high CH. Evaporation and refill will only increase the CH over time. It is lowered by water dilution if the CH of the fill water is lower than that of the pool water. It can also be lowered by reverse osmosis (RO) though companies using that process may not be available in your area.

To deal with high CH you can target a significantly lower TA level and a lower pH, but it will be hard to keep the pH lower unless you lower the TA. The use of 50 ppm Borates in the pool can help keep the pH from rising as quickly, if that has been happening. There are also metal sequestrant products that primarily sequester calcium (they're called scale inhibitors), but that would be a last resort if you've tried everything else.

Can you please post a full set of test numbers -- pH, TA, CH, CYA, Temp and whether this is a salt pool and whether you use borates? From this post you listed "TH" implying Total Hardness, but the TF-100 doesn't test for that so was that a typo? You also noted 400 ppm, but now you are saying 750-800 so I'm confused. Your TA (120) and pH (7.8-8.0) readings were high. You can use The Pool Calculator to calculate the saturation index. If I use the 400 ppm CH reading plus your other readings (assuming 7.8 for pH from your range) and assume 70ºF water temperature, I get +0.42 for the saturation index. If I use 800 ppm CH and 8.0 for pH, I get +0.84 for the saturation index. This is why you are seeing scaling -- the light brown tan stain on the walls and floor of the pool as well as white crust on the tiles.

If you were to lower your TA level to 70 ppm and get your pH target down to 7.7 then the saturation index would be in balance at +0.04. However, you'll want to remove the scale you already have so to do that you'll want to significantly lower your pH (making the saturation index negative, at least temporarily to remove scale), but if that scale redissolves it will increase your CH level even further.

thanks for the help chem geek, those readings i had done before were done with test strips, since then i got a test kit and readings are ph 7.6, ta 100, CH 750, cya 60. current water temp here is 60f-64f, i will test my fill water tonight, and lets say it comes back in the ideal range, what would be my next step to lower the CH ? thanks alot chem geek

Let us know the CH of your tap water. In this post you say you are from south Arkansas. According to this map, Arkansas is not a horribly high hardness water area (looks like 61-120 TH in south Arkansas). Either your pool had an extraordinary amount of evaporation and refill with minimal water dilution or someone used Cal-Hypo as a source of chlorine over an extended period of time. I'm hoping your tap/fill water is low enough in CH that you can use partial drain/refill to lower your CH level.

yea, from south ark chem geek, we moved in around early aug, the pool looked good, but not sure what was being used as far as chlorine goes, the guy had a floater in there is all i know....if my tap water is ok to do a partial drain and fill, do i need to perform the drain and fill now or wait to the spring? also, my pool is roughly 20,000 gall, how far down would i have to drain the pool before i refill it ?

The previous owner probably went the Pool Store route: trichlor in a floater and a weekly dose of Cal-hypo "shock".

How much you replace depends on the CH of the fill water. If it were zero, it would be simple math. Another factor to consider is, do you close the pool up and cover it? If not, winter rains will dilute it, and rainwater is zero CH. When we have a storm coming, I drain some water out and direct one of my downspouts into the pool. Yes, I get a lot of dirt and sediment, but that can be vacuumed out.

It is possible, and I do it, to use pool water to water the lawns and then refill. More work, but it helps keep CH down, and I was under water restrictions last year so I didn't have much choice.

ok guys, rechecked the CH last nite and this time i got it in the 550 range, and the fill water to the pool is 150 CH, do you guys recommend me doing a partial drain and fill ? or just leave it alone ?

What was different about your testing?

i think the first time i tested i didnt stir it up enough i guess, not really sure

Accurate testing is a key to good pool water management. I suggest you do the test once more hoping to repeat one result or the other.

If you repeat something close to 550, I suggest you drain about 1/3 of your pool and refill. If water is cheap, I would do the 1/3 drain a second time and then you should be down around 300 or so.

Importantly, keep your pH ALWAYS in the mid 7's and your TA down around 100 or perhaps a little less. That'll help any tendency to form calcium.

I don't know where you live (post that) but I assume your swim season is over.

live in south ark, water temp is about 60 right now, first yr owning a pool and i'm gona keep it open through the winter..

Yeah, if you're gonna' keep it open, I would drain at least 1/3. Rainwater will probably take care of the rest getting it below 400. Keeping your pH and TA at the above levels and checking that frequently will help prevent any further scaling.