Getting your first pool ,and learning how to clean it yourself, can be quite confusing at first. Learning how to vacuum properly and efficiently is probably the most important thing to learn and wondering if you can vacuum a pool on backwash is not an unreasonable question.
You can vacuum a pool on backwash, in theory at least, but it would have no benefit. The water would be pumped backwards through the filter, trapping much of the dirt, before passing out through the backwash hose. This dirt would then end up back in the pool once the pump was back on the filter setting.
I will try and explain why it would not be worthwhile to vacuum on backwash fully so that you can understand better.
Why shouldn’t you vacuum on backwash?
The reason for this is that when the multiport valve is in the backwash setting the water flows from the pump into the bottom of the sand filter, rather than the top as it does normally. Then the water passes through the sand or filter medium to the top and out of the waste pipe into the yard, down the drain or wherever your pool expels water to. In doing so it takes any dirt that has been trapped in the top layers of sand and expels it, therefore cleaning the sand.
If you were to vacuum a pool on backwash then all of the dirt you pick up from the pool would mainly get lodged in the bottom layers of the sand and stay there. When you then put the multiport valve back to filter, after you had finished vacuuming, then much of the dirt that had become trapped in the bottom of the sand filter would be pumped back into the pool.
Also, while you were vacuuming on backwash, all of the water would go to the waste pipe so the water level would drop pretty rapidly, just as it would when deliberately vacuuming to waste when a pool is very dirty.
Which settings to use to vacuum a pool
There are only two settings on the multiport valve to use to vacuum a pool and which one you would use largely depends on how dirty the pool is.
Vacuum a pool on filter setting
This is the setting you will use most frequently. You would vacuum on this setting for your routine cleaning when the pool is not very dirty. When you use this setting the dirt is trapped in the sand, or whatever filter medium you have, and clean water returns to the pool via the return jets.
You would often then backwash the filter for a few minutes to clean out this dirt before returning to the filter setting.
Vacuum a pool on waste setting
You would generally only use this setting if the pool is very dirty, perhaps when you do the first clean of the year after the winter or if you had a period of very bad weather when lots of debris ended up in the pool.
See my post How to vacuum a pool to waste to read more.
Can you backwash a pool while vacuuming?
I sometimes have to stop while I am vacuuming my pool on the filter setting (so the water is passing through the sand filter) because the suction begins to reduce. This is due to the sand in the filter becoming clogged which reduces the amount of water that can pass through the sand increasing the back pressure. You can often tell if this is the problem as the reading on the pressure gauge is likely to be higher than normal because of it.
To restore the suction I switch off the pump and then move the multiport valve to the backwash setting. I then run the pump again for a few minutes to remove the dirt that is blocking the sand and then resume vacuuming once I have put the multiport valve back to the filter setting.
I leave the vacuum hose connected to the skimmer port while I do this so no air gets into the system and I can resume vacuuming straight away after the backwash. Read my full step by step backwash guide for further details.
You may find the following articles useful, particularly if you are a new pool owner. I have tried to answer most of the questions that I had when I first bought my house which came with an in-ground pool with a sand filter system.
My top three pool cleaning tools to make life easier
Dolphin Nautilus CC Plus Robotic Pool Cleaner – the best time saving product on the market. I have never heard anyone say they regret buying one.
Hayward Poolvac Leaf Canister – very useful when leaves are a problem in your pool
Aquatix Pto Pool Step & Corner Vacuum Head – I use this every time I vacuum my pool. It gets where other vacuum heads can’t.
If you have a pool, you probably wonder about the best practices for maintaining the right chemical balance in the water, especially when it rains. You might ask yourself questions about what...
Shocking a pool is part of the regular pool maintenance that needs to be carried out to keep the water quality in good condition. It is important to know when is it safe to go back in the pool after...