Can Chlorine and other common pool chemicals make your pet sick?
Overexposure to chemicals, including chlorine is always something to be careful and mindful of. Dogs in particular have a keen sense of smell, it is particularly important to be mindful of how you handle and store pool chemicals, for your pet safety.
Salt Water, Pool Chemicals and Sunscreen lotion all pose a threat to your pet. Excessive time in salt water is never good for humans, and the same is true for dogs. Salt Poisoning is known as hypernatremia. Symptoms include vomiting and diarrhea. Hypernatremia can become worse and cause seizures, depression, in-coordination and brain swelling. If your dog is with you at the beach or near a salty body of water, be sure to pack plenty of water for the day, and keep him hydrated, so he won't be tempted to drink from the ocean or a salt water pool. 
Algaecides, Antifreeze and clarifiers are not considered harmful when they are properly diluted in the pool water. When they are not diluted or broken down into the water they are corrosive and dangerous. They may have a sweet odor, and if spilled, a dog may lick up a liquid pool chemical. If ingested they can cause mouth ulcers and damage the GI tract with life-threatening punctures. This is why it is especially important to have chemicals properly stored and locked away.
Most animals will not digest chlorine products or dry pool chemicals that you may have to adjust the water balance. However, chlorine tablets and shock should be securely stored in a dry, cool area. Pool stabilizer (cyanuric acid), or dry acids used for pH control could also be dangerous if ingested. Chlorine diluted in the pool water however, can irritate the skin and eyes and dogs can get infections if they spend longer periods of time in the pool. Skin rashes can be experienced in worse fashion than in humans because the moisture is trapped in the fur of the dog, and can take months to heal. 
Ingesting large amounts of sunscreen oil is toxic because of the various ingredients that include salicylic acid, laxatives, zinc oxide and PABA. Gastroenteritis, bone marrow changes and liver damage are some of the most severe complications that can occur due to the ingestion of sunscreen oils and tanning lotions. Use only sunscreen specifically made for dogs.
Dogs aren’t always as quick as humans when it comes to learning some things – such as closing your mouth to avoid swallowing large amounts of chlorinated water. Chlorine can cause burning of the throat which works its way down to the dogs’ digestive system.
Because they ingest the chlorine, like anything else that is poisonous to a dog, the body wants to get rid of it because it can’t handle the heavy chlorine or salt, therefore they get sick and try to remove the poison from their body. 
There are also products that even when ingested, will not provide a problem of toxic ingredients. As another form of prevention, it could be helpful to consider some of the products from Natural Chemistry and Sea-Klear. Clarifiers, Enzymes and Phosphate removers are all natural and eco-friendly, and they reduce chlorine demand.
To further reduce pool chlorine reliance, or to maintain it at a low level, you can add Mineral Purifiers by Nature2 or Frog, or install a Del Eclipse Ozonator. Either system can reduce your chlorine demand by as much as 50%, when water is balanced and filtered properly. These systems are available for both inground and above ground swimming pools.
There are safer forms of DE filter powder too. Not that your dog would rip open the bag of DE and spread it all over the room (or would he?). DE has been shown to be a mild carcinogen in tests with lab mice, and can cause respiratory difficulty if inhaled. AquaPerl is a cellulose, paper pulp filter media that is safer to store and use than diatomaceous earth.
What are some easy ways to prevent a dog from getting into the pool chemicals? Constant supervision is always a primary safety measure, but making sure pool chemicals are not in reach of pets is vital. This simple task prevents health problems or emergency visits to the vet.
If a dog does swim in chlorinated water, be sure to thoroughly rinse the coat and dry after each swim. This reduces the odds of skin allergies from developing. Keep a fresh bowl of drinking water around for the dog near the pool to cleanse the throat. This also helps prevent your dog from drinking gulps of water in the pool because of thirst. Finally, a reduce your chlorine use for safer swimming, by using supplemental sanitizers, and keeping your pool water balanced and a little over-filtered.
Give your pet a pat for me!
SPP Pool Pet Expert
 "Summertime Pet Poisoning Hazards." Petinsurance.com health article.
 "Could The Chlorine In Your Pool Make Your Dog Sick? - Bellas House & Pet Sitting, Scottsdale, Az