Are you controlling the level? Or simply monitoring it?
It sounds like you might have your Set Point (or Target Level) too close to the High Alarm Level.
It also sounds like you might have a high Slosh-Factor. Slosh is the effect you see on the ocean when the waves are choppy as opposed to when the waves are virtually non-existent; Rough Seas (high Slosh) vs. Smooth Seas (low Slosh).
You might need to control the Alarm Condition in Ladder instead of in the Alarm Function.
An aside regarding Slosh...
This effect can affect Pressure Transducers as well as Float-type Transducers...
This is a general description in terms of Float-type.
The rougher the surface and the smaller the surace area of the detector, the harder it is to determine an average level. The level of the surface, at any given point, in a tank with a high Slosh-Factor, will be chaotic. The wave action might be periodic, but the timing of the readings are not likely to be in-sync.
Even if you increase the number of samples taken before judgement is made (without taking so many samples that your response is too far behind), there is no reason for you to believe that the readings will be reasonably and properly distributed across the range of possible readings so as to produce a reasonable and consistent average.
Float sizes can range from a very large percentage of total fluid surface area to a very small percentage.
At one extreme, if you had a large float that covered the entire area of the tank you would get a very good average indication under any Slosh conditions. However, you might have problems if the average level changes by large percentages in small periods.
At the other extreme, if you used a pin-float to measure the level of a fluid with a high Slosh-Factor, you would be reading the crests, troughs and points in-between. At the same time, the float would actually be accelerated upward or downward at times, thus giving an even more bogus indication.
The lower the Slosh-Factor, the smaller a float you can get away with. If the Slosh-Factor is at or near zero, you could get a good reading from a pin-float.
If you have a tank with a high Slosh-Factor, you could install a float with a larger surface area, or you could (might be able to) install a baffle to reduce the Slosh-Factor.