TDS and Calcium Hardness


New member
Dec 6, 2018
San Diego, CA
New to the site, but wanted to get some suggestions to compare with what I'm getting from the local pool store.

My pool is an in ground pebble-tec pool with about 8,000-10,000 gallons in it. We've owned the house for almost 7 years. Pool filter is standard DE and we run a hayward pool vac. 1st couple years of pool ownership was a learning curve. Took all the advice from the pool store and most of it didn't work. Used chlorine tabs, and was regularly brushing/vacuuming the pool during the summer to get rid of algae on the walls. After that switched to liquid chlorine (10%) and added it as needed along with small amounts of muriatic acid to keep the PH in check. Normally in the summer months when the pool temps are in the low-mid 80's I would add about 2 gal of chlorine per week to keep chlorine at about 2-4ppm. In the winter when water temps were low it would be more like 2 gal a month. This past season I have had to add quite a bit more chlorine (3-4 gal/week) to keep the same levels. I also noticed that the pool water tasty slightly salty, and all our friends were convinced we had a saltwater pool. I would normally take the water into the pool store a couple times a year to be checked, but haven't done so in a while. I finally got around to it and these were their results: FAC=0, TAC=0, CH=1000, CYA=99, TA=70, PH=7.8, Acid=2, Copper=0, Iron=0, TDS=8800, Phosphates=2500.

The water in my pool is crystal clear, and was that way all summer. In the summer I run the filter about 4 hours a day and in the winter about 1 hour a day. Pool company said that the high levels of dissolved solids including salt means that I need to add more chlorine to keep levels in check which is what has been happening. They recommend that I drain the pool and refill. This test was 2 months ago, and since I was thinking of maybe draining the pool since it's been almost 8 years since it was last drained (right before we bought the house), I have been pretty lax on adding chlorine. I know there have been periods of days, even a week or more where there was no chlorine in the pool and still have not had any algae. I clean the filter every 3-4 months, and there is algae on the screens, but none on the pool walls or steps. I know this is a lot of info, but just trying to be thorough.

Basically I'd like to know if you think I should drain the pool water an refill? It seems amazing to me that I am not doing much and the pool is still crystal clear. I hate to drain the pool and deal with the expense of new water when my pool is maintaining nice clear water with very little maintenance. Am I missing something?

Thanks in advance for your advice.


Gold Supporter
TFP Guide
Jul 21, 2013
Northern NJ
Welcome to TFP.

Algae on your screens indicates there is algae in your water. A properly sanitized pool has no indication of algae in the water.

Your CYA is likely not 99 but much higher. 99 is all the pool store test can go up to. We do not put much stock in pool store water tests since they are found to be unreliable and unrepeatable. You need to get your own test kit like the TF-100 Test Kit â„¢ or Taylor K-2006C.

Since your CYA is over 90 you will need to follow the instructions in Step 8 at Pool School - CYA to determine the actual CYA value in your pool water .

You are getting the right advice to drain your pool for the wrong reason. You must get your CYA down to a manageable level. The only way to get rid of CYA is by draining and diluting it in the pool. How much water you need to drain depends on the results of a proper CYA test.

Once you get your CYA down to around 30-50 you can then your pool water to eliminate the algae. When the is complete you can use TFP methods going forward.

I suggest you read Pool School - ABCs of Pool Water Chemistry and Trouble Free Pool School

That is the big picture of your problems. There is much more for you to learn here if you decide to apply the TFP methods to your pool care going forward.

If you choose to hang around here please Read This BEFORE You Post and put the details of your pool in your signature. It will help us give you specific advice on your situation.


Mod Squad
TFP Expert
LifeTime Supporter
May 11, 2014
Franklin, NC
Welcome to the TFP pool! :splash:

We find that many times pool store employees primary goal is to sell stuff, not necessarily get your pool in perfect condition. As to whether that is because of improper training, lack of knowledge or just to sell stuff I will leave up to you. While you would think that a "professional" would be the best, unfortunately in most cases it is quite the opposite. Between employees who blindly trust the word of chemical sales representatives and high school kids working in the pool store for the summer you end up with poor results from their advice and testing.

Unfortunately the pool industry has evolved into sales by scare tactics, misdirection, misinformation and marketing hype. Go in to the store and tell them your TA is low and they are going to sell you baking soda in a fancy package at four times the cost of WalMart. Do they have a right to make a profit, yes - but lets be reasonable. Heck, even their definition of "low" can many times put you on a pH roller coaster that's hard to get off of. Is that lack of knowledge or a sales technique to sell you more chemicals to control your pH????

In your case they have settled on TDS and phosphates to direct you to for your problems. I can promise you, they are not your problem. A big part of your TDS number is your elevated CYA. CYA appears not only in the individual,test for it, but also as part of the TDS.

To know what is going on with your pool we need accurate test results we can trust, and those don't come from a pool store. We base our pool care system on your personal accurate testing and only adding what the pool needs, when it needs it. To do that you need your own accurate test kit. Order a TF100 test kit.

The only other real option for a test kit is a Taylor K-2006-C. Be careful comparing prices because the K-2006 comes in sizes, designated by a letter. The basic K-2006 has .75oz bottles. You need to get the K-2006-C to get the larger bottles that you want. Even then it is a little short on the reagent & powder for the FAS/DPD test.

Please don't go back to the pool store for a test kit. To effectively practice the TFPC methods, the FAS/DPD chlorine test is essential. The TF100 test kit and the K2006C have this test while very few other kits do. The kits sold at the pool store generally won't won't cut it, but be careful pool store employees are known to say “it's the same thing”. Generally it's not!

While entirely optional, I also have the SpeedStir and Sample Sizer. They speed testing and accuracy.

Once you have your own test kit we can move forward, but while you wait for it you can start by a minimum of 33% drain/refill to get the CYA down. After that no more solid forms of chlorine. Tabs and shock are almost 50% CYA.

How much Pool School have you read? Start with these:
ABCs of Water Chemistry
Recommended Pool Chemicals
How to Chlorinate Your Pool

So, welcome to TFP!!


Gold Supporter
TFP Guide
Nov 12, 2017
Central California
Hi Pez! Welcome to TFP!!

You're getting some great advice form Allen and Tim. Get the test kit. Be prepared to replace some water. Stay out of pool stores.

I did the same, and installed some new equipment, and my pool is an absolute joy. I haven't had to add chlorine or acid (by hand) since mid-summer last. Just imagine. No algae, perfect balance, crystal clear water. Do study up here, and add your signature, and you, too, can experience the smooth sailing of TFP...


Mod Squad
LifeTime Supporter
Jan 17, 2012
Evans, Georgia
I'm sort of surprised your pool is crystal clear considering that FC and CYA, and that you don't have a bit of scale problem with that much calcium!

Folks who follow the TFP method here do learn ways to monitor and work to prevent scale when they have such high CH as well as high evaporation rates which also acts to raise CH (evaporation takes the water but leaves calcium, salts, and CYA behind).

If you want to test our distrust of pool store testing just take 3 samples of water to 3 unrelated pool stores and you'll most likely get 3 different results. Which one to trust?

I would drain and refill just to get that CH down, the CYA down and start fresh with our methods. But owner testing is the investment in your pool care that is the most important element. I personally have the TF-100 test kit, available from Pool Supplies, Spa Supplies and Parts or

Some folks come back and later tell us that they *thought* their pools were clear but after starting our methods they're surprised at how clear things got!

Maddie :flower:


New member
Dec 6, 2018
San Diego, CA
Hi guys,

Thanks for the quick responses. I've been on the site a bunch as an observer, not a poster, so have read pool school and do have a taylor K-2006 testing kit. The pool store definitely screwed up my CYA reading. It hasn't been above 40 for years. Just went out and did a test on my own kit and here are the results:

FAC=1.8, TAC=2, CC=0.2, PH=7.6, TA=60, CYA=less than 30(tester marks only went to 30 and said to see when you could no longer see black dot in tube. Water was crystal clear and when I added it all the way to the top of the small test tube I could still see the black dot fine). CH=1100.

I will update my signature with the pertinent info. Any new advice on whether to drain or not would be appreciated.



Gold Supporter
TFP Guide
Jul 21, 2013
Northern NJ
Calculate your CSI using . You need your water temp for CSI calculation.

With CH at 1100+ you will probably need to drain to get it down.

Test your fill water for CH. You should figure put where the high CH is coming from.

With CYA 20 your FC is below the minimum of 2 and should be between 3-5. See [FC/CYA][/FC/CYA]. That is probably why you see algae around your pool.

With the algae you see you should do an and probably the pool.