Hi Warkovision:
I've responded to this type of question a number of times on this forum using what works for me, so I'll repost here in an effort to help you as well. I have a large tub (500 GAL) that gets pretty heavy use on a weekly basis. The ONLY time I get foamy water is when the water is "dirty." Generally, it gets foamy when a bunch of “dissolved solids” (not the chemical type) get mixed up in the tub water.
Before you start worrying about a chemical problem, try this method. First, go to your local Lowes (if you live near one) and buy a product called "Super Clear Clarifier" by AquaEZ (the big BLUE bottle, about $8.00 and it lasts a LONG time, see link below). This product (or another like it) is a highly concentrated “cationic polymer” that will "clump" the CRAP out of the stuff in your tub. From what I can tell, it’s also pH neutral. Similar products are available at other stores.
Turn the tub on and adjust the diverter valves so that the surface water (and foam) is directed into the filter box through the weir door. Add 3 to 6 caps of the blue stuff to the water while the tub is running. Don’t be afraid to add more than the instructions say, it won’t work like I indicate unless you use quite a bit. Keep a small bucket of water and a cotton rag handy to wipe out the nasty stuff that will appear in the filter box.
Very shortly, the tub will start to foam. It may even push right out of the top of the tub. Scoop the foam out of the tub if it becomes a problem. The reason why the water is foaming is because it contains dissolved oils that create surface tension and ultimately cause millions of small bubbles to form. The process is similar to shaking up a bottle of Italian salad dressing containing both vinegar and oil. After the tub begins to foam, you will probably see orange/brown/grey "stuff" clumping in the foam and running into your filter. Some of this stuff may also be deposited on the tub walls. GET RID OF IT! Use the wet cotton cloth and wipe it out, followed by rinsing the cloth in the bucket. This “STUFF” is what comes out of people’s skin (sun tan lotion, deodorants, moisturizing agents, dissolved fats, dead skin, dirt, etc., YEAH, I know, that’s GROSS). Keep the tub running for about 30 minutes. If the water is REALLY bad, foam will continue to form. At some point you might consider adding anti-foam if it gets too bad, but try to avoid this because it defeats our purpose. Also consider closing the air injection valves.
After the tub runs one cycle, pull the filters and REALLY clean them using a filter cleaning solution and a garden hose. Use the hose on "stream" and REALLY blast the crap out of the filter, especially in the ends of the pleats. Replace the filters and let the tub run an additional cycle. Stop the pumps and let the water settle for about 15 minutes. At this point, the water should be clear. If not, repeat the treatment again. Consider doing this every weekend if you use the tub daily.
After you finish "cleaning" the water, re-install the filters and add shock. I recommend an all-in-one vinyl pool shock treatment that contains an oxidizer, a sanitizer (dichlor), a buffer, a clarifying agent and a flocculent (see
"Enhanced Shock" from SpaGuard or “Shock Plus” available at K-Mart stores). I add this product after using my tub and “shock” with a bigger dose on the weekend. My maintenance dose is about ¾ a shot glass nightly.
If this method doesn’t keep the water clear, your problem might be chemical in nature. From what you wrote, it sounds like your base level of sanitation is too low. Consider doubling or even tripling the amount of dichlor product you are using. Low levels of sanitation can be tricky when using a "mineral purifier" (I use Nature2), because "extra use" or "no use" over several days can push your equilibrium levels out of whack. I generally "over-sanitize" in these cases to avoid problems.
PH and calcium levels could also be an issue here, so test and make certain they are within acceptable range.
I recommend this method of water treatment because I've used it to make “clean” water in less than two hours out of water that looked so BAD you couldn't see the bottom of the tub. Hopefully, it may work for you as well.
A product link to the clarifier agent (blue stuff) is
http://www.aquaez.com/sub_chemicals.html.
Hope this helps. Post questions if you have them.
Good Luck!
Drewski