Hi Posting General Science, as I think this group will know my answer and the topic might be fun for educators.
I want to build a solar pool ionizer and have some questions. First, my assumptions and a description.
I am assuming I'll need to be able to reverse polarity so that one neither electrode is plated by the other. Most of my reading says to use copper plumbing pipe as the electrodes, however, too much copper can stain the pool, and blonde hair. Also, copper is effective in ridding a subset of microorganisms than silver.

The device started simply with a solar panel connected to two electrodes (copper pipe) held in close proximity, but not touching, using a set of zip ties for both spacing, by wrapping around 1 electrode, as well as holding the pair together, by binding the two together. The wired connections would be inside of a sealed plastic container with the electrode protruding. This would both float and be water proof.

1. In a 2014 thread, there was mention of need a resistor in case the water was too conductive and diminished the voltage. How do I test this need, where do I test the voltage in the circuit. And where in the circuit is the resistor needed.
2. to avoid plating bias on the electrodes, I will add an automated polarity reverser. Any suggestion on ho to do this?
3. does reversing the polarity change the resistor placement?
4. To minimize cost and the chance of staining the pool, can one electrode be silver, while the second copper?
5. Finally, how much voltage do I need to realistically create colloid in a quantity to keep 15k gallons of water microbe free?

 

I want to build a solar pool ionizer ...

Why? There are many models available commercially. Generally speaking for DIY, it'll cost you more in time and money to make your own when there is a competitive market for a product.

I am assuming I'll need to be able to reverse polarity so that one neither electrode is plated by the other.

While that sounds reasonable, it is an assumption. I'd take a look at the commercial units to see how/if they solve this problem, which may not be a problem.

The device started simply with a solar panel connected to two electrodes (copper pipe) held in close proximity, but not touching, using a set of zip ties for both spacing, by wrapping around 1 electrode, as well as holding the pair together, by binding the two together.

Are you sure this is the most effective configuration? The commercial units don't look like this.

1. In a 2014 thread, there was mention of need a resistor in case the water was too conductive and diminished the voltage. How do I test this need, where do I test the voltage in the circuit. And where in the circuit is the resistor needed.

It may be true that to drive copper off the electrode and into the water that you need a minimum voltage. The resistor idea assumes you might get too high a current between your electrodes, pulling the solar supply voltage too low to cause copper release. Maybe. This is a fairly complex electrochemical situation and I think it would help to better pin down the factors at play before designing the circuit. That caveat aside, the resistor - if needed - would be in series with the load. I frankly doubt it would have the desired effect.

2. to avoid plating bias on the electrodes, I will add an automated polarity reverser. Any suggestion on ho to do this?

That's called an H-Bridge, just like you'd use in an RC car to reverse the motor. You could put it under control of an oscillator to reverse the polarity, say, every minute.

3. does reversing the polarity change the resistor placement?

Nope

4. To minimize cost and the chance of staining the pool, can one electrode be silver, while the second copper?

Yes, but that much silver will be costly. And the staining is the result of the total concentration of copper, which will be a function of how much current you drive into the electrode. Hard to predict, in other words. I believe people use test strips to monitor copper level.

5. Finally, how much voltage do I need to realistically create colloid in a quantity to keep 15k gallons of water microbe free?

You're not creating colloid, just soluble copper ions. Above that possible minimum level mentioned earlier, voltage won't matter much - it's current.

 

First, do a Duck-Duck-Go-Search for .........
"Copper and Silver Pool",
then come back with the peak output Voltage of the Solar-Panel(s) you are using.

The only reason to have any concern over the Voltage is to protect the Electronics from over-Voltage.
You don't need "Voltage", You need a "Current-Regulator" and a polarity-flipping-Oscillator-Circuit.

The Surface-Area of the Electrodes,
the Water-Flow-Rate,
the spacing between the Electrodes, (which must be kept precise),
the Conductivity of the Water,
the available Average-Voltage,
and amount of time at a workable-Voltage,
Water Ph, and Calcium-Hardness,
all have to be maintained within workable ranges.

THERE IS NO HIGH QUALITY, "LOW-MAINTENANCE" SOLUTION, PERIOD.

Fortunately, if You can generate roughly ~30-Volts for ~8-Hours out of the day,
the adjustable "Current-Regulator" will take care of
keeping things consistent, and within an acceptable, effective range.

The Current-Requirements are VERY LOW, ( roughly ~20ma ),
and, if necessary,
a cheap, commercial Boost-Converter can be used to increase the available Voltage to ~30-Volts.

If Current in excess of ~40ma is used,
the end-result will be actual chunks of metal being ripped off of the Electrodes,
rather than creating extremely effective Colloids of the Metals,
which, by the way, can not be separated from the Water.

Once effective levels of Copper and Silver are attained,
Current must be reduced to a very low "Maintenance-Level",
probably on the order of around ~5ma. or so,
to make up for Water "Splash-Out" or leakage.

Absolutely stupid-high-levels of Copper are required to cause any perceptible color change.
Copper-Levels this high may be hazardous to your Health.

Silver has "zero" toxicity at any concentration/level, and will not cause any color changes.

Chlorine, Electrically created in the Water, and requiring the addition of Salt,
is EXTREMELY EFFECTIVE when used correctly,
unfortunately, very few people, virtually no one, knows how to use it correctly.
Used properly, it is virtually impossible to detect it's presence in the Water,
and is THE most effective Pool-Cleaner/Sanitizer ever devised, ( when used correctly ).

Don't try any of this if You have EVER used any commercial product that contains Chlorine-Stabilizer,
and almost all commercial Pool-Products contain it.
2-COMPLETE WATER CHANGES are required to remove all "Stabilizers", and have enjoyable Pool-Water.
"Sequestering-Agents" will NOT remove Chlorine-Stabilizers,
( but they are very effective for other Water problems, especially "Water-Turbidity" ( cloudiness ) ).
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