Here is a exerpt from an article I did on finding a leak in SpaRetailer
"First off, let’s talk about types of insulation. Contrary to what is often preached on the sales floors, it’s not any easier to fix a leak in a “Thermopane” or partial-foam spa than it is to fix in a full-foam. Both can be work, but both need to be diagnosed differently.
In both spas, your first step is to look for discoloration, damage to the cabinet or obvious mold or calcium collection around the base. Depending on the pitch of the pad, this will give you a side to start on. Also, have the customer shut the spa off and let it leak until it stops and you can see what jets or fittings are on that level. This will give you a height to look at once you’re in the cabinet.
At this point, on a fully-foamed spa you can either remove the panel or tip the spa up on-end and feel under the spa for soaked foam. For me, this is a benefit of the full-foam because I can feel the amount of water and know I’m getting close. The discoloration will increase the closer you get to the leak, so look for dark yellow, brown or even black areas. If the leak is fresh, you might need to use a dye to actually discolor the foam before draining
the spa. You could save a lot of time by having your customer pick up dye and add it to the water a day or so before you come out. Make sure they know how to use it and that they first remove any pillows or items that are permeable from the spa.
In a partial-foam spa you’re more likely to see calcification around the area where the leak is. However, don’t be fooled by water traveling to the low-hanging pipes and collecting calcium there. Look for yellow or brown in the water spots and you should be getting close. You can also use dye in a partial-foam spa, but I suggest looking for the calcium first. Don’t count on feeling for the leak in this type of cabinet because the water often travels along the pipe. This is a much bigger problem in a spa that has just a small amount of insulation over the plumbing because the outer shell of the insulation hardens and forms a path. Between the cabinet heat and air exposure, the flexible plumbing can become stiff, brittle and impossible to move or re-glue. In that case, you will need to follow the plumbing to the next good point.
If a spa has hose clamps, it can make things easier to see, just look for rust stains along the plumbing or in the insulation.
One of the most important things you can do for yourself when detecting leaks is to use good lighting."
