Maybe it's the trays you're using? Forgive the store references - I'm sure they're different from those you have in New Zealand! I'll try to take a few photos when I'm in the yard and add them to this post.
Here are the 3 types of trays I'm experimenting with:
I've got the large plastic containers spring mix comes in, I buy organic spinach from Sam's for $4 and keep the container. Those work great.
I'm using clear Rubbermaid food storage containers that are long and shallow, they come with red lids. They're too expensive to buy for this but I had them already.
Lastly, I bought aluminum turkey roasting pans from Aldi for $1 each because they're very sturdy and other "sprouters" have used them with great success.
The holes I poke in depend on the size of seed. Since I tried alfalfa I needed very small holes so the seed doesn't fall through them.
Hole tip: poke them through from the inside because the hole forms a little "lip" of plastic and that affects drainage. That little ridge of plastic (or aluminum) keeps more water in the bottom of the pan, which leads to rot.
