I'm a complete newb compared to most here, and I have been searching but haven't found anything that exactly matches my situation. Please bear with me.
My pool is about 8 years old (specs in signature), and the last couple of years have been difficult to maintain it. The first problem I had started last year. Basically what happens is, the system works fine for a few hours, (sometimes even less than an hour), and then you start to see gradually more and more bubbles coming out of the return jets, and the pressure coming out of those jets gets lower and lower. At the same time, the pressure on the gauge at the filter, which normally reads 18psi when the pool jets are on, starts to rise and eventually gets up to 30psi. When it hits this mark, the pressure at the return jets is nothing more than a trickle of bubbles. Same thing when you switch over to the spa jets as well. There is just very little pressure coming out of the jets.
When you look at the pump basket, it appears to only be about half full. You can see the water streaming into the pump basket through the intake pipe, that's how low the water gets. Yet even with this, the pressure at the filter is still around 30psi, nearly twice what it should be. You can also hear a "gurgling" sound coming from the top of the filter. It almost sounds like when you open the purge valve a little bit. I've tried purging it, but it has no effect.
Now, if I run a backwash cycle, even for just a few seconds, everything goes back to normal for a while. Pressure is normal, and there is a good stream of pressure coming out of the return jets, with just a small stream of bubbles. It stays like this for a while, and then eventually it falls off again. Sometimes it goes away after a few hours, sometimes less than that.
Other issues that I notice...after backwashing there are some bubbles and water swirling around the top of the pump basket. More than what I used to see back when the pool was working properly. I used to be able to see the bottom of the basket even when the pump was on, with maybe just a small bubble or two at the top, whereas now the bottom of the basket is blurred by the bubbles and water swirling. However, when you turn the pump off, the water stays in the basket and pump most of the time. Other times it will sounds like air is released inside the filter and the pump basket empties about half way. I had a bad o-ring a couple years ago and had the same symptoms but the pump lost pressure immediately and the water drained out of it when you shut it off.
I'll tell you what I've done so far. Last year I was reading somewhere that it will have these symptoms with low jet pressure when the sand needs to be changed. So I found a guide on changing the sand, and I emptied the sand filter, and replaced the sand with a new batch of pool filter sand.
The problem was still there. Then I started to slowly develop a problem with water seeping out of the backwash line. So I got tired of dealing with the hassle and just shut the pool down early last year, and haven't messed with it until this week.
I had been doing some reading and realized the spider gasket on my multiport valve was probably the culprit for my leak in the backwash line. Upon inspecting the gasket, it was definitely bad, no doubt about it. Well, the base of my multiport was discontinued so yesterday I purchased a new multiport valve and installed it. This solved the problem with my leaky filter, and I was hoping that somehow it would magically correct the other problem but it didn't. At this point I don't see any leaks anywhere. My return line does have a corner it turns before entering the chlorine charger, and I will see a drop or two every few seconds coming from that fitting, but that's it.
In addition to making sure the skimmer and pump baskets were clean, I also checked and lubed the pump basket lid o-ring, and also lubed the o-ring at the pump impeller. I inspected the big pump gasket that goes between the two halves and it looks fine. There are no cracks or crushed areas in any of the pump o-rings or gaskets that I've looked at.
So at this point I'm kind of at a loss. I kind of limped along last year with it like this, and actually got the pool swimmable, but when the pressure starts going down, I notice it doesn't even fill up the canister with the chlorine tablets, so the water doesn't stay clean, and it becomes extraordinarily difficult to maintain. I really don't want to go through that again. Any advice or help you can offer would be appreciated more than words can ever convey. Thank you for taking the time to read this.