Question on Pool Skimmer ports

[missourian]

I have been owning this pool since last August but after a reading a post in TFP it motivated me to go and see the skimmer inlets

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Of the two ports

1. The one marked in Red is what pulling the water to the pump
2. The one marked in Black arrow, I am not sure why it is there, I see it is filled with DE (I tried with a tiny stick)

Both of my skimmers exactly the same, I don't know the use of the dead port (The port marked with black arrow). Also, recently I switched my values in such a way that;
a. pool main drain fully open,
b. skimmer one fully open,
c. skimmer two fully open,
d. Spa main drain fully closed

I noticed skimming efficiency reduced a lot(the force of water sucked into the skimmers is reduced).

Can someone help me in understanding my system?

 

[Richard320]

Since you have a valve to isolate the main drain, my guess is that that black port is connected to nowhere. The DE just settled in there when they added it too fast. Stick the garden hose in there when the skimmer is sucking and it should flush the DE out and the skimmer will draw it away.

Reduced skimmer action is because you have all the drains open. Your pump can only move so much water so fast. I'd close down the main drain about 80%. It's really only useful to prevent temperature stratification. I will confess to putting my pool on full drain when brushing, so hopefully what I've pushed down there gets sucked away. Keep the spa drain closed unless you are in spa only mode.

If your weirs (skimmer flappers) are waterlogged and sunken or missing, that will also decrease skimmer action.

 

[missourian]

thanks Richard