Troubleshooting filter?

[mbwalker]

I've been struggling with startup on my pool since late April and not sure what to try next. I have a 22,000 gallon in-ground with 3/4HP Hayward Super Pump and S-244T sand filter. The pool is 13 years old, all original equipment. Live in NC, operate pool 5 months per year.

When I started up I had an algae problem and also an issue with lack of pressure at filter. Per conversations on this board back in April (this thread: lack-of-pressure-t20349.html), it was suggested that my problem had to do with a blockage or some sort or air leak centering on pump. I did the following: replaced o-ring on pump strainer basket, purchased and used pool lube, checked impeller (ok), checked weir (ok), checked for leaks (found none).

After all that, the pump did seem to be working better (no bubbles at top), so I began the shock process to get rid of algae. Maintained chlorine at 15 to 20 as best I could for two weeks. Algae obviously killed (color went from bright to dull green), but water was not clearing up. I was concerned that during this time the pressure at my filter remained at or near zero, despite the pump working fine and little or no air bubbles in pool. Moreover, during this time, the filter NEVER needed backwashing. I did backwash every few days during this period, but water was almost totally clean (unlike previous year's, where filter would need backwashing frequently during startup).

Based on that observation, I concluded that the culprit was the sand in my filter. (14 years old, never replaced). So I replaced the sand (vacuumed out old and replaced with new). The filter's backwashing mechanism seemed to work fine (I backwashed after replacing the sand), but after a few days with new sand, I noticed no change in the pressure level on the filter and a subsequent backwash didn't reveal any particles. I assumed my problem was particles suspended in the water, so tried a clarifier, but it made no difference. Two days ago, I resumed shocking -- no signs of new algae growth, but didn't know what else to try.

I'm contemplating replacing the filter totally, but not sure if that's the solution. I don't know anything about how water flows through a filter, but is there a way to test to see if there's some sort of mechanical problem there? No leaks around multiport valve, which seems to be working fine. I did replace the gasket when I replaced the sand. And replaced the pressure gauge.

Current numbers are CYA 45, TA 100, CA 20 (low, but don't think it matters), FC 16.5, CC .5
The numbers are as of this morning after overnight test, FC last night was 17.

Sorry for the lengthy post, but wanted to give as much information as possible in hopes that someone could suggest something else to try.

 

[duraleigh]

mb,

That's an informative post and paints a good picture of what's been happening. First of all, I doubt it's your filter.

Secondly, would you post back to these questions?

1. What is your current psi? Does the psi drop to zero when you turn the pump off?

2. When you replaced the sand, do you feel you put in the amount needed....it's usually somewhere around 2/3 full for optimum.

3. How long has the FC been at that high level (when did you put that chlorine in the pool)?

4. Describe how your water looks right now.

5. What's your pH?

 

[mbwalker]

1. PSI is zero or very close to zero. Never has gotten higher than that. When I turn off and switch valve to backwash, I don't hear whoosh of pressure, like I do when things are normal.

2. Put in 300 pounds of sand, which is what Hayward said my filter would require.

3. I've been putting chlorine in several times a day for a month now. I've done my best to keep FC at or above 15 for a month (though it did drop to around 10 or so once or twice when I was at work or when I shut down to replace the sand in the filter).

4. Water is light green. Floor of pool not visible. When I started it was definitely darker green and visibility was lower than it is now, so there's some improvement.

5. pH currently tests at 7.8. I've read on TFP that the test is not reliable at high chlorine levels. When I started it was at 7.2. I have added a little soda ash a couple of times during the month (my pool normally runs pH high).

Two more things that may or may not be relevant:

1. I run the pool vacuum (Zodiac Alpha G4) a few hours a day. There's no problem with pulling enough pressure to use the vacuum.

2. Last year I had my liner replaced. I used to have two intake locations (skimmer and pool bottom), but it was changed to only one when the liner was replaced. (?!?)

Thanks for any suggestions you can give.

 

[duraleigh]

I think your psi guage is defective. If you have enough flow to vacuum properly and flow back into the pool seems normal, your psi should usually be somewhere around 10-16 on most all pools. The guage is inexpensive (less than $10) and it is essential that you have one that works well.

Meanwhile, light green means you did not kill all the algae. I suspect you are fighting an algae bloom but not quite holding your FC high enough or consistently long enough to completely clear your pool. Shocking is a process that can take several consecutive days. I read from your posts that you have been doing that but I want to emphasize how important it is to understand that FC levels need to be very high (around 15-20ppm in your case) and held there constantly until your pool clears. It will absolutely work.....it always does. It simply takes longer than most people think and the need to hold the FC constantly high is often overlooked.

Your filter, pump and all parameters look fine to me. I see no equipment issues (other than the pressure guage) and I would not consider replacing the filter. Chlorine and lot's of it applied consistantly is the answer to clearing your pool.

 

[mbwalker]

I think your psi guage is defective. If you have enough flow to vacuum properly and flow back into the pool seems normal, your psi should usually be somewhere around 10-16 on most all pools. The guage is inexpensive (less than $10) and it is essential that you have one that works well.

Well, I guess the gauge could be defective, but I've already replaced it once a few weeks ago. Normally, it runs around 8 and I back wash when it gets close to 20. But they're cheap enough to go buy another and give it a try.

Meanwhile, light green means you did not kill all the algae. I suspect you are fighting an algae bloom but not quite holding your FC high enough or consistently long enough to completely clear your pool. Shocking is a process that can take several consecutive days. I read from your posts that you have been doing that but I want to emphasize how important it is to understand that FC levels need to be very high (around 15-20ppm in your case) and held there constantly until your pool clears. It will absolutely work.....it always does. It simply takes longer than most people think and the need to hold the FC constantly high is often overlooked.

Your filter, pump and all parameters look fine to me. I see no equipment issues (other than the pressure guage) and I would not consider replacing the filter. Chlorine and lot's of it applied consistantly is the answer to clearing your pool.

Hope you're right. Clorox is cheaper than a new filter. I've been shooting for 15 to 20, but will aim a little higher and try to keep it above 20. Worst algae problem I've had since the pool was built 13 years ago.

Thanks for suggestions.