I am a complete newbie and have had a new pool for a year now. I am indebted to TFP for everything I now know. This is my first post, but I have been reading extensively here for the last year. I have never had the need to ask a question since I have invariably found the answer to every question I have had. I can't thank the members here enough for their questions and answers.
Since my wife doesn't like saltwater pools, I settled on bleach as my chlorine source. I obtained a Liquidator with which I suffered a very steep learning curve. I had all the problems described here with "white stuff" plugging hoses and valves, air leaks, etc. My chlorine delivery was so intermittent that I developed a black algae problem. Thanks to TFP, I have been able to get this all under control and become a confident and knowledgeable pool operator, today.
Every three days or so, I had to add about a gallon of acid to the pool. Of all my chores, handling hydrochloric acid is the most odious. It seems like I am always downwind of the stuff, trying to hold my breath, hacking and coughing. I wanted an acid feeder. I just couldn't understand why the equipment cost was so high. One of the available products required half-strength acid and I didn't like the idea of diluting the acid and having to replenish the supply twice as often. I decided to build my own acid feeder.
Dispensing a corrosive chemical like concentrated HCl against pressure requires a peristaltic pump, mainly to keep the acid away from the mechanical parts of the pump. Most of the pumps that I found after extensive Internet searching were not only quite expensive ($500+) but also unable to operate at the low flow-rate that I required. There is also the problem of finding a pump designed to use tubing that is chemically resistant in addition to displaying characteristics consistent with peristaltic operation (flexible but able to withstand suction pressure without collapsing).
I finally found a workable solution at a very good price point, SimplyPumps.com, Model PM216.
This pump uses 0.625"ID tubing with a flow rate of 35 ml/min minimum at 25 psi and suction lift of 20 feet. They can supply the pump with viton tubing which will work with the concentrated acid. The pump with the Viton tube set is $103. A 2-pack of replacement Viton tube sets is $22. Less expensive tubing can be used for supply and delivery. They also provide variable speed PWM power supplies for their pumps. The unit I bought for my pump sold for $24.
Rather than using the adjustable feature of the power supply, I chose to control the motor speed with the voltage control feature of the power supply. I found the control voltage that produced reliable pump operation and built a simple constant voltage supply for it. I control the amount of acid delivered with a solid state duty-cycle controller meant for heating and AC control.
The pump has been in use for about 2 months and holds the pH constant at 7.5 at 10% duty factor. I have not yet done any testing of the pH in the pool return during the on phase of the pump. The outflow of the pump is threaded into the 2" PVC return pipe with a 1/16"ID X 1/8"NPT adapter. I'm sure there will be a pH spike, but I expect that it will be acceptable, due to the high flow in the return pipe.
I adjust my Liquidator (10% bleach) with another duty-cycle controller connected to a 3/8" (1/4"ID) solenoid valve that keeps the pool chlorine at 6.0 with a setting of 4%. I have found that the larger ID is much less sensitive to debris than the standard flow meter.
After a year of effort, with the help of TFP, I can now leave town for a couple of weeks without having an expert watch my pool. It remains to be seen how all the parts hold up. I am checking Cl and pH daily. Necessary maintenance is an unknown at this point.
If anyone is interested, I would be glad to produce an article with details and photos about what has worked for me, if I can figure out how to do it on this system.
