For normal diarhea I just give amodium but I would be more concerned with the pale gums.
No , the algae problem is still out there. They had warnings on the radio just last week as several dogs had just died from it. As stated, pale gums on a dog that normally has good color is a bad sign. One reason owners should always check their dog's gums when they know the dog is healthy so they know what is normal for their dog. Pale gums can show early signs of shock or other circulation problems. You can also check capillary refill by pressing against the gums with your thumb. When you take the thumb away the color should return instantly. Any delay is a bad sign.
I would call the vet again and let them know about the gum color. You said that you brought him to a vet. I assume they did a blood work up. If not, they should. Xrays or ultra-sound may also be considered. If he isn't drinking enough he may need IV fluids. Is he showing any other signs of distress ? IE: can't get comfortable, pacing, panting more than normal, repeated stretching of his hind legs ? Any of these can indicate abdominal pain. Speaking of which, when you palpate his stomach , is it turgid or does it bring about a pain reaction ?
good luck,
dave b