Back pressure went up, then down...why?

[PrivatePilot]

Ok, new to the pool world but I have a good grasp on most stuff mechanical.

Yesterday we had a huge pool party in several waves - adults in the morning and teens in the afternoon. All went great, I ran the filter full time all day as expectedly the swimmer load was crazy high. As the day progressed I noticed the back pressure building as I expected it would - I normally run 7PSI with a the filter clean, and it crept up - 10 psi around afternoon, 12 by dinner, and close to 16 or so by sunset. I figured I'd be in for a backwash today after letting the filter run a good portion of the night to polish the water up again (as it did, things look nice and clear again this morning), but what surprised me was that I checked back pressure today and Its dropped back to about 9psi as of this morning.

I thought once it came up it would stay up, no? Did the filter cycling on and off after its nightly run cycle (I have it on a timer) allow debris to "resettle" in the sand and flow improved, or something?

Is this normal?

 

[mas985]

That kind of PSI rise in a single day is not normal and usually indicates an algae bloom or a super dirty pool.

It could be a problem with the filter gauge. If it happens again, tap the gauge and see if it changes settings. Also, does the gauge go to zero when the pump shuts off.

Lastly, filter pressure can also be affected by the valve settings.

 

[PrivatePilot]

No algae or even a hint thereof, pool started the day crystal clear and shimmering, and is probably 75% back that way today.

Bather load was, as mentioned, crazy wild all day long - between the first and second "wave" of the party the water clearly had clouded up somewhat and the skimmer was pulling a lot of crud off the surface of the water. This is only a 12x16 that probably saw 20 swimmers in the morning (many who got in/out a lot) and then in the evening 12 rambunctious teenagers who also got in and out quite a lot for about a 4 hour swim session.

I had no idea what to expect for a backpressure increase (this was our first official, and big, pool party test), but I expected it to rise. I had no idea that that much would be abnormal in a day. The gauge does return to zero nicely when the pump shuts off with no issue, and there's no valve issues or other restrictions.. Up until yesterday I had never saw it over 7-8 where it hovers consistently. For the most part it's settled back to about 8-9 PSI today as of now.

 

[mas985]

What type of filter do you have and what size?

Were people wearing a lot of suntan lotion? Any oil slick on the surface?

 

[PrivatePilot]

Hayward Pro LX 1HP pump and Hayward Pro S180T filter (150lbs of sand). And yes, sunscreen was plentiful yesterday as it was hot and sunny, and there was definitely a slick on the surface after the first wave of swimmers in the morning. It got cloudy in the afternoon so the teen crowd was less on the sunscreen, but still had some without doubt.