The issue at hand beyond current handling is the reverse voltage spike produced when the inductive load is switched. You can put a dedicated surge arrestor power bar off the sonoff and then plug the pool filter into that
please no big words 
. You can put a dedicated surge arrestor power bar off the sonoff and then plug the pool filter into that
if you can please put this in more noob terms
and thank you!
This pump will melt the 16A relay pretty soon. The starting current would be in a range of 30 to 50A. I also tend to derate the Chinese relays by at least factor 2. You are better using a motor contactor that you control with some cheaper WiFi switch.
Tell us more about the existing relay … with a view to re-using that by controlling it, leaving the power side wiring alone.
That’s a good point however an earlier post in this thread suggested that newer motors limit startup current, and therefore this may not be in issue here. Need to lookup the motor datasheet to confirm.
However as DarkoG mentioned, the startup current might fry the sonoff, and therefore it would be wise to use the sonoff to power a motor contractor (solid state relay), then that relay would operate the pump.
In case it is inverter driven, no issues, assuming the inverter is set to limit the current to nominal. However if not, the newer motors with higher efficiency class have bigger starting currents, and on top of this you need to take the inrush spike that can be 20x the nominal. Simple relay 16A might work, but how long?
In my applications involving a pump I use contactors, controlled by some cheap WiFi or other switch. True it comes at cost but I feel it is the right way to do.
umm … that would tak out 99% of the home fuses, which for outlets are rarely more than 20A … it’s unlikely that high
Doesn’t work like that. Fuses and breakers are rated by time as well as overload, most will tolerate brief startup overload by design. (And you select the sensitivity)
will only the relay break? i am preapred to live with that …
can this damge the pump in anyway ?
i will do it the right way once i will figure it out…
i had a feeling that a chip sonoff will not go so far… i once conncted my A/C to a sonoff and it was also a short story for the realy
You told us the pump is already controlled by some existing relay, and I presume that is working fine.
Why not continue to use the same existing relay, by working out a way to have the sonoff or whatever switch the existing relay, not the pump directly.
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its more of a clock/day timer , that goes in the power box
somthing like this…
not sure how to achive this? shuld i take a pic? 
@rossko57 @DarkoG
what do you guys say about this realy ? i am sure its not an award winning product but will it solve my issue? its rated for 50A and it goes nice in the box 
image|405x435
Do you have wiring diagram?
The timer relay on the photo seems like rated for 16A. As @rossko57 mentioned, you could also keep the original timer and set the it to be always ON. You could then connect cheap Sonoff in series with the L & N terminals shown right on the photo. In this way you could control your pump by controlling the Sonoff
Okay,if it is one of these
it is a mechanical timer, with cams physically pushing the heavy duty switch around.
Won’t be able to control that from the low power side, so that’s out.
The timer contacts are 16A rated, I’d be inclined to substitute a 16A Sonoff.
I’d use the Sonoff, as @rossko57 said that time clock is only 16 amp. Plus your pump is only 975 watt full load so your probably covered on the startup/inrush
General rule for inductive is 225%, which would give you about 9.53 amps startup
If you look at the datsheet of that timer you can see that it can start 4A at power factor 0.6 or 16A at pf 1. That motor is 975W so the nominal current can be about 4.3A even if the power factor of the motor is 1, but normally during starting the power factor is in range .2 to .3 and the induction motors have starting current of 6 to10 times the nominal. I have feeling that timer is underdesigned or there is some more powerful relay behind it. No idea what are the Sonoff limits when starting inductive loads
Just had a quick search, the motor is CSIR or PSC with separate start windings so the cap is going to limit the in rush. Page 23. (Start windings about 12 amp)
Best thing… stick a clamp meter on it set to max and see what you get.
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I use a Sonoff TH10 with tasmota firmware and waterproof temperatute sensor. So can control via mqtt and have a view on the water temperature too. Worked well last year.
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I agree, measuring the start current is the way to go