How to fill the pentair rainbow 320

Oct 28, 2014
San Jose, CA

I'm just beginning to learn how to maintain my pool. I have a stupid question about how to use the in-line pentair rainbow 320 chlorine feeder. I've followed the instructions: closed the control valve, then stopped the pump, waited, then restarted the pump, then opened the lid. The tube was mostly empty, but there was a small amount of water on the bottom of the tube.

So am I really supposed to drop in the tablets into that water? I've read the chlorine tablet warnings, and they are absolutely clear about one thing: I should never add small amounts of water to the tablets: might react violently, etc. But that is exactly what will happen when I drop the tablet in: the tablet will arrive in a small amount of water.

Moreover, even if I get inventive, and open the lid when the pump is not running, to let all the water drain out of the tube, only then insert the tablets and close the lid, I still have the same problem: when I start the pump and reopen the control valve, a very small stream of water will enter the stack of tablets. I'd say that counts as "small amount of water".

So what's the solution? Am I missing something, or am I just too cautious in obeying the choline tablet warnings?



Mod Squad
TFP Expert
LifeTime Supporter
Apr 17, 2010
East Texas
I assure you they won't self-explode! (won't even fizz like alka seltzer tablets) Plop them in and fire it up. Welcome to the forum.


TFP Expert
Mar 2, 2011
Tabs won't react violently to water. The two main concerns that I would be cautious about would be water splashing out if the tablet were dropped into the water because the water can be high in chlorine and would not be good to get in the eyes or face.

The other concern would be that the feeder screen at the bottom could be damaged by a falling tab.

I would suggest getting some disposable gloves to handle the tabs and lower the tab to the water or bottom of the feeder if it's empty.

The warnings are about getting water in the bucket of tabs. In that case, the tabs will begin to dissolve and create chlorinated vapors. Even then, they wouldn't explode.

Also note that while tabs can be useful, it's usually not a good idea to rely on them exclusively. Long-term they can cause problems if not managed properly. When you have time, you might want to check out Pool School for more information.
Oct 28, 2014
San Jose, CA
Thanks guys, this gives me a lot of confidence now to continue :) I'll be careful not to splash the water out.

James, yes, I have SWCG, but now that the water temperature dropped to 61F, it shut off (low salt). I measured 2800-2900 ppm salt (with Taylor titration test). I'll add salt, but my local pool store convinced me that the cell won't work below 65F, even if I add salt. Reading the Pentair Intellichlor manual, it should work as far down as 52F, but regardless, I think I'll get through some time with using trichlor tablets, because the pool has close to 0 CYA right now. I'll see how fast it grows, but I'll continue with the tablets until I reach the TFPC recommended 70-80 ppm CYA. I might even boost CYA up to 20 by adding stabilizer directly.