fiberglass pool won't hold chlorine and starting to have small stains

[Alisha]

I'm excited to be a new member of the TFP gang! I have 2 problems right now. The pool won't hold chlorine very long, I'm adding a gallon of liquid chlorine every night before bed. Also, I'm starting to see some small copper looking stains that I can't seem to get rid of. The water is crystal clear only because I stay on top of it and test my water twice a day like a crazy woman. Here is my reading tonight about an hour after pouring a gallon of liquid chlorine in.
FC- 3.5
CC- 0.5
PH- 7.3
TA- 90
CH- 200
CYA- 90

I know I need to get my CYA down. Is that what has a hold on my chlorine? I switched over to liquid chlorine and said goodbye to pucks about 2 weeks ago- have not used a puck since, but am adding a gallon of chlorine a night. Is that normal? Would the liquid chlorine be causing any of the copper looking stains? My calcium hardness was low for about 2 weeks and the pool store told me that I didn't have to add CH to a fiberglass pool. When I started to see some staining, I quickly purchased some CH just in case that's what was causing the problems. Does a fiberglass pool still need CH? S
Sorry for all the questions! I'm just excited to be finished with the rip off of the pool store!

 

[Beens]

Hi! Just a quick reply to get you started....

Which testing kit are you using?

My question is going to be in reference to your CYA reading. In the extended test kit directions - See number 8. There are instructions for testing your water if the cya is 90 or above. Have you seen/done that extended test? It could be that your CYA is even higher than you think.

Pool School - CYA

I think it might be a good idea to try to figure that out first. You are going to need a much higher FC if your CYA is really that high. It will be best to start the process to lower it. You'll need to get a decent idea of how high it is so you'll know exactly what you need to do to get it to a more manageable level.

and... Welcome to TFP!

Others who know more than me can help with CH and staining! ;-)

 

[Alisha]

Thank you for the quick response. I used the Taylor Kit FAS-DPD. I have not tried the extended test. I will do that and get back to you.
Another question.... How much liquid chlorine is too much to pour in at one time? Is it ok to pour in a couple gallons at once to begin SLAMing once I get my CYA down? Or is that much chlorine at one time hard on the pool surface and equipment? And what FC level is too high to be swimming in?

 

[Jezza]

Welcome to TFP.

The appropriate chlorine level is relative to the amount of CYA that you have in your pool. You can also swim at the SLAM/shock level for your pool as per this FC/CYA chart. If for example you were at 90 CYA then it would be safe to swim up to 35 FC.

The best way to pour chlorine into the pool is slowly in front of a return. Use Poolmath to help you work out what you want to add.

In theory the addition of calcium is to protect your gelcoat in a fiberglass pool if it has calcium carbonate. TFP does recommend a level of 220-320 for fiberglass pools as a precautionary measure and if you have hard water that doesn't tend to be too much of an issue- more of keeping the levels down.

Just wondering how you think you might have gotten copper in your pool?

 

[Alisha]

Not sure about the copper or even if that's what the stains are. They look like little rust stains, small little dots, they just appeared- nothing has fallen into the pool or anything like that. I've tried the vitamin C tablets, that did not work. I also use a weekly dose of Metal Free to avoid any staining. I've been using a cap full of Metal Free once a week since I opened the pool in April.

 

[Alisha]

so to get my FC up to 35 would take A LOT of bleach if it is only at 3.5 now, right??? How many gallons can I add at one time or do I add a small amount every hour?

 

[Beens]

Run that test on your CYA first it might be higher than 90. It would be best to replace water to lower it so it's easier to maintain.

You can add a whole lot of bleach, slowly, one jug at a time as long as you're not going above your SLAM level. That will depend on the CYA.

You could add 3498723232 jugs of bleach if you needed to (haha you won't need *that* much) all at the same time as long as you're pouring it slowly in front of a return so it has a chance to mix in as you pour it.

It all depends on the CYA level.

Get that extended test done so you can see what level of FC you need. If your cya is really 90 you're going to need at least 7FC to maintain it so you don't end up going green. If your chlorine is not holding overnight you're going to need to do a SLAM which is going to require a whole lot of bleach if your CYA is 90+. Best to SLAM at closer to 30 CYA.

 

[Alisha]

Thank you, I'm draining water and adding in some fresh right now. I'll test the CYA tonight (both tests) and post new results. The chlorine didn't hold at all overnight. I was back to 0 this morning after adding a gallon of liquid chlorine last night. I added another gallon this morning and it has surprisingly held while the sun has been beating on it all day. When you guys say a FC of 35 does that really mean 35? Or are we talking about 3.5? sorry, I'm just confused. I've read that you're not suppose to swim with a FC of 6 or higher. Is that true?

 

[Jezza]

A common misconception is that FC of say 5 or 6 is high but often the same people that quote this as a fact fail to acknowledge the FC/CYA relationship. That is the level of FC and whether it is high or low is directly proportional to the amount of CYA.

CYA buffers the harshness of chlorine and FC of 3 with 0 CYA is harsher than 35 FC with 90 CYA.