Maintaining of a sand filter
With a sand filter, you should definitely perform a backwash (minimum every three weeks, this can also be more) and after 5 years you should replace the sand from the filter with new sand. 
If the sand filter has not been circulating for a long time, the sand will start to stick together and you will have to replace the sand. 
Besides backwashing and replacing sand, you should also put superflock plus in your skimmer. Superflock plus is a flocculant in the form of a candle that is used in sand filters for effective prevention and removal of turbidity in the water. Due to its patented formula, superflock plus dissolves slowly, creating a long-lasting effect. Use superflock weekly for optimal results.

The different settings of a swimming pool sand filter
A sand filter always has a 6-way valve, because six different modes of operation are possible with the sand filter. 
Please remember: If you change the mode, you should always switch off the pump! If you don't do this, your pump may be damaged. 

1. Filter: Filtering the pool water. The water goed via the pump to the sand filter. The clean, filtered pool water then exits the sand filter back into the pool. 
2. Waste (empty): This is to drain all the water out of the pool. This is only necessary when the pool is very dirty and needs a thorough cleaning. 
3. Backwash: ‘washing the water back'. This is to clean the sand filter. The water goes out in the opposite direction (into the sewer or another place). 
To backwash, you must first turn off the pump! Then first set the 6-way valve to backwash and switch the pump on. The water now flow in the opposite direction. Backwashing takes 1-3 minutes. If you look through the sight glass of the sand filter and the water is clear again, it's sufficient. 
4. Rinse: The six-way valve should be placed in this position immediately after backwashing. You do this for 30 seconds. On the rinse position, the water goes from the top to the bottom while it's discharged into the sewerage. In this way, all the sand is returned to its place. 
5. Circulate: This position is to mix certain products with the pool water as quickly as possible. The water is drawn in by the pump, but does not pass through the sand filter. 
6. Closed: Now all outlets are closed. You must now turn off your pump as quickly as possible, because the pressure builds up rapidly. The closed position is mainly used when working on the sand filter. 

In short, the 6-way valve is usually on the 'filter' position. 

The basis for your clean pool
The filter and pool pump are the basis for obtaining clean filtered water. 
To obtain and keep the water clear and clean, it's important that the pool water is pumped through a (sand) filter by means of a pump. 
If you would not filter the wter, bacteria, algae and fungi get a chance to develop in the pool water and adding products to your pool water is not very useful. 

Filter pump and sand filter in one unit
To properly filter your pool, you need a pump and (sand) filter. 
The pump ensures that the pool water goes through the filter. 
We, at Stesha Wellness, offer 2 sand filter pumps that er filter and pump in one, 2 in 1!
The Onda Filtration kit is a 2 in 1 model adn the Intex sand filter is also a 2 in 1 model. 

How much flow rate should my filter or pump have? To know how much flow rate your pool and pump must have, there is a general rule: volume of the pool in cubic meters (m³) divided by four.
So: number  m³ : 4 = the necessary flow
E.G: 18 m³ : 4 = 4.50/m³. For this you must then take a pump and/or filter that is at least as heavy, certainly not lower! It's always better to have some margin than to calculate with a small margin. 
Here you can be sure that the water is sufficiently filtered and the more the water is filtered, the better the quality of the pool water.