Most sailplanes are designed around heavier NiCD battery packs and heavy motors, so if you are putting in a LiPo pack it is not unusual to find that you have to add a lot of weight to the nose to offset the long tail.

If possible make the additional weight "usable" weight, by using a larger heavier pack, and moving things as far foward as possible.

Also remember that weight added to the nose ( e.g. a heavier spinner ) has a larger lever moment, requiring less overall weight to move the C.G. forward.