[clydesdaleclopper]

SlimJim as Waddy says humidity only needs to be high for the last few days once internal pipping has happened. As it is early in the year the eggs tend to be less porous and so it is more difficult for them to lose the required weight to allow the air sac to be big enough.

[midtown]

Currently, I've got an outside humidity reading of 74%, indoors it's 55%.
You're in the hands of the weather gods, and the only way to solve the problem would be by using a dehumidifier.
I think it's quite important that you not only rely on the humidity reading of the incubator, but also to have a separate humidity reader located elsewhere in the room to read the ambient humidity.

The fact the incubator is located in a tack room may be the answer to the high humidity reading - leather breathes, and will also attract moisture. Think of a bridle hung over a period of time without use? It doesn't take that long before mould spores become visible. Similarly, in a overly dry atmosphere the leather will dry out and become unworkable unless we put 'moisture' back in. 

[clydesdaleclopper]

I think a dehumidifier is probably the best option but I think it would be too expensive.

[Womble]

CC, try buying dehumidifying resin sachets from Ebay and the like. Put a couple inside the incubator and it will bring the humidity down. They can then be regenerated in a warm oven and re-used.

[cloddopper]

just an idle thought .
Would a black heat bulb inside a big cardboard box set over the incubator make enough heat to dry the air a wee bit to bring the humidity down enough ?

We have one of the Delonghi type dehumidifiers in the caravan on a two hour on 6 hrs off time switch cycle .

It fair drags out the moisture in the air if it is set to high .. they cost about £95 on eBay .
We also use it to dry big item washing hung over a table type drying rack .