Question
    I've had this plant for 4-5 years now and it was large when I got it; sending up runners as long as 4 feet, leaves 3-4 inches wide and 12-18 inches long.
    The second year I had this plant it flowered, the third it flower twice in one season. But it hasn't flowered for almost two years.
   The older leaves have always had  these dried light brown spots on them; irregular shaped, 3-4 in. long by 1 1/2-3 in. wide with only two to three spots per leaf. It reminds me a little of shot-hole fungus, but I've never heard of that as a problem for cacti and keep my watering at the appropriate level for most cacti. 1-2 times a week to be exact.
    Within the last year the older leaves have been turning yellow,the spots are spreading to the younger leaves, and are getting larger.  
    The yellowing of the leaves has been persisting even after I repotted and lightly fertilized with a time release 10-10-10.
    The plant has had a western exposure for a year now, through a glass door, at least 6-8 hours of sun a day. I think I many have burned it once a few years ago, but I don't think this problem is sun related.
    I love this plant very much and its poor turn in health has me very worried, please help me save my plant!

Answer
Kim,

Cactus should be bone dry before you water it, you should be able to insert a bamboo skewer into the soil all the way to the bottom and have it com out dry. Watering it once or twice a week is way too often unless you are only giving it 1/4th of a cup of water at a time. I really suspect the yellow leaves are coming from overwatering.

Is this cactus in a sandy cactus soil or standard black potting soil? It should not be in black potting soil and it should not be in a pot with a diameter larger than 10 inches. The pot must have a drain 2 wage hole and when you water it you must empty the drain tray an hour after watering it. I water mine once every 2 weeks in the summer and once a month in the winter.  I agree that the problem is not sun related, it needs as much sun as possible, the location is fine.  Cut back on watering and it will improve. If you have more questions feel free to write again. Good luck.

Darlene