Koh Si Chang is a short ferry trip from Sri Racha, near Pattaya, and well worth a day of your time if you want some respite from traffic and bustle on the mainland
We boarded one of the several ferries at the Sri Racha pier and were on the island within one hour. The pier on Koh SI Chang has a long line of waiting tuk tuks and we hired a six seater for the day at a cost of B250.
Although the island is small, a day trip is enough for only a glimpse of what it offers. Inevitably, the first stop suggested by the driver was the Chinese temple. A walk up the steps or a ride in the small and unsafe looking funicular provides a view over the town.
The temple has some interest but is as much a trap for tourists' cash as anything else with its several opportunities to but oil and incense. The Buddha cave is a little whacky for my taste.

But the dragon guardians are quite dramatic.

Although the town is pleasant enough to walk around, perhaps something like a Thai version of a Cornish fishing village, the best part of the day for me was lunch and relaxation on Tam Pang Beach. There was a good range of seafood there, better than on the mainland and with no unpleasant after effects. Koh Si Chang's coastline is not sandy except in this one spot so I imagine that weekdays are the best days on which to be sure of a seat under the canopy of umbrellas. We were one of only two groups on the beach.

Koh Si Chang is not blessed with many resorts, being a place for a day trip rather than an overnight stay. However, our tuk tuk did pass one or two resorts so a few strokes on an internet search engine should provide information for anyone planning to stay.