Diarrhea in older horses -- like Harv

Harv has fairly consistent diarrhea. It is not continuous, but 75% of the time he seems to have loose poops that I can't explain. I've heard that as teeth are less effective, hay is harder to digest, and cubed hay is indicated. I'd hate to do this, so I'm trying a few other things first. I bought some Platinum Bio-Sponge, which has been well-reviewed for helping digestive issues. An eight-day supply was $30. Apparently it absorbs toxins, viruses, bacteria and free radicals, and other bad stuff. There is research to support its effectiveness in resolving diarrhea. But it seems to me it is more symptom control and does not address the cause of diarrhea directly. This may be okay in many cases.

I gave it to Harv for the first time a few days ago. It has made a difference! But it is not the easiest to administer. Here are a few tips...

• It's the consistency of powdered sugar, but apparently not as good-tasting. The instructions say "top dress" but you have to feed about 2/3 or 3/4 cup twice a day. Harvey, who I feel would happily consume scrap iron, gave up on his top-dressed feed after a valiant try.  SOLUTION: Mix with apple sauce and mix in their regular feed. At least, it worked on Harv. Riley would probably need a slurry.
• The smallest tub lasts eight days, after which you determine if it worked, or will work. I read online that the manufacturer says you can feed it long term in lower doses (e.g., half the amount, twice a day). Unless your horse is in critical condition, this may work.
• If you have questions about administration, call 1 (800) 553-2400or email clients@platinumperformance.com. I've heard that they are very helpful and responsive.

I'll give a full report at the end of the administration period. But I do think Harv is better.