Keeping the Chlorine up and light yellow stains

This is my first year with our new inground pool. I'm having some problems keeping my water clear and with a light yellow stain that appears from time to time on all the whole pool. Here are the specifics on my pool:
17,000
Pentiar IC40 SWG
fiberglass
sand filter

This is the history:
1. left the pool open over the winter because it wasn't done and couldn't cover it.
2. Looked pretty bad in the Spring but was able to get up and running and looking real good in about 2 weeks of working on it
3. Had to replace the new concrete deck because the pool company did such a bad job so I was doing a LOT of vacuuming to get all of the concrete up.
4. within a couple weeks of starting the pool up I started to get a light yellow stain on the built-in seat bottoms and the stairs. I read on here that I could use crushed up Vitamin C to take the stains off. This worked great!!! So, I went ahead and treated the pool with 2 pounds of ascorbic acid as described on here. Afterwards I treated it with a Sequestering agent.
5. Pool went cloudy about a few days later. (we also had about 5 people in the pool over that weekend, and some dirt got into the pool as well because we aren't totally landscaped yet) The cloudiness was bad enough that I couldn't see the bottom on the 3' end. The color of the cloudiness was white, but it had a slightly aqua green tint to it.
6. Shocked it with about 4 packets of HTH shock and brought it back to clear.
7. Had about 7-8 people in the pool and again the pool went cloudy
8. Shocked it again with 4 packets and it's starting to clear up, but today I've noticed that I'm getting the light yellow whole pool stain back. Sprinkled a little Ascorbic acid on the spots and it's coming off.

The only thing that I've noticed is that my Chlorine level never gets above a .5 or a 1 unless I shock it. Is this normal for a SWG? Then, when I do get the chlorine up, the pool seems to yellow faster (almost overnight).

Here are my chemical numbers as of right now. I have three kits (2 test strip based and 1 chemical based - for the most part that I do back up each other's results)

Total Chlorine 2
Free Chlorine 2
PH 7.0
Alk 100
CYA 30-50
Hardness 250
Salt 3360

Okay, so why doesn't my chlorine level get about .5 or 1 without the help of shock? what is causing this thing to cloud up so often (weekly), and what is causing the light yellow stain to keep reappearing (every 2 weeks or so).

Thanks for your help!!!!

Jon

Looks like your pH is a little low which is interesting since most of the time SWG's usually creep your pH up. Sounds to me like your IC40 may not producing enough Chlorine... what setting do you have it set at? How did you test your CYA? With your SWG running, test your water right at your return.. it should be dark yellow/orange, if it is, something tells me that some sort of algae is consuming your chlorine quickly and you need to shock. You probably want to use liquid bleach to get your Chlorine up to 15ppm since you have a CYA of 30-50. Keep brushing the pool on a daily basis and test your water 2-3 times a day and keep the shock level up. Once your Chlorine level holds to 15ppm overnight you can let it lower itself to 3-5ppm. Vacumn any dead algae or debris and backwash/rinse. You hopefully should have a clear pool by then. you can use your IC40 to shock if you press the two buttons together, but most people like to save the wear and tear on their SWG's and use liquid bleach instead, its your choice.

One thing I don't see mentioned here is the higher CYA requirements listed in the manuals for SWGs. I have an aqualogic and the owner's manual lists ideal CYA levels between 60-80 PPM. According to the pentair web site they recommend CYA between 50-75 PPM. I've noticed much better chlorine production when my CYA levels are in this range.

Look at page 11 of the owner's manual for you SWG

http://www.pentairpool.com/misc/owne...lor_Owners.pdf

How long ago did you do the stain treatment? Using ascorbic acid can make it hard to keep a chlorine level for a while, because the chlorine is used up getting rid if the ascorbic acid. It will also lower your ph and alkalilnity. You have to keep your chorine very steady after a stain treatment so that you do not have to shock. You should not shock for at least 2 weeks after an ascorbic acid treatment. You also have to add borax to get your ph back into range, but for now I would leave the ph low and add more sequestereing agent. It may be enough to lighten the stains. Sequestering agents sometimes lower ph also. If not just pour a little ascorbic acid where you see the staining. When the stain is gone, start to balance the water and keep adding chlorine (I use bleach so that I can control the amount) until you get to 5 - 6ppms. Try not to let it get lower, and don't get it up to shock which at a cya of 30 - 50 would be 15ppms. Let me know if you have any other questions:)