There are lots of great ideas in this thread. Just keep in mind that some experiments are hard to do in small water volumes. If you get a 50 gallon trash can and fill it with pool water (you can use a submersible pump and hose for doing that) you can get more stability. Let me comment on each of the experiments mentioned since it will likely come down to doing what is practical.
FC degradation due to sun exposure with varying CYA levels or FC/CYA ratios
This is a fairly easy experiment to do using a FAS-DPD chlorine test kit since you can use a 25 ml water sample to get 0.2 ppm FC resolution. In addition to varying FC and CYA levels, you also need to control for water depth so have both shallow and deeper containers large enough to be exposed to sunlight (it would be hard to lower the CYA level if one used the swimming pool). You'll need a control for each depth that is not exposed to sunlight.
Analysis of the results will be challenging, however, since the chemistry is complicated and it doesn't tease out the different effects of protection between chlorine from it being bound to CYA vs. any CYA or CYA-Cl UV shielding effects.
I witnessed a test of distilled water vs tap water vs treated water. The theory is water does NOT conduct electricity. Minerals in water conduct electricity. I have set up that proves this. Just a thought. Write if your interested.
This should be a very easy experiment to do if you have a conductivity meter. If you use a standard multimeter, that won't work well because the probes used could have electrolysis and such resistance tests use DC while to lessen electrolysis effects you'd want to use AC. You'd probably want to use a standard conductivity meter since building your own will be challenging to determine absolute numbers given plate areas, distance, etc. though you could use such a homemade system for relative measurements.
How does the out gassing rate of CO2 and subsequent pH rise scale with different forms of aeration (return jets, bubblers, spa spillways, waterfalls)?
For this experiment one would need enough of a pH swing to be accurate enough with the pH test unless you use an electronic meter that you calibrate regularly. If possible, you want to get a control/baseline with a pool cover since the pH can also rise from other sources such as from plaster, especially if it is newer.
I would be interested in seeing if CYA make water more opaque to UV light. Perhaps a graph of UV opacity vs increasing CYA levels.
This would be one of the most useful experiments for us here on the forum since it answers a fundamental question and can lead to better modeling, but it is also more difficult or costly since it requires some way of measuring UV, preferably with a spectrophotometer. If your daughter can contact a nearby university and see if they have one in one of their labs that she could use, they might be willing to accommodate. For this test, not only should CYA in water at levels found in pools be used (so say 30 ppm, 50 ppm, 80 ppm), but there should be tests with and without FC as well since it's possible that the chlorine bound to CYA absorbs more. Note that the UV spectrum we are interested in is that from sunlight that makes it to the ground so 300-380 nm which is higher than traditional UV spectrophotometric measurements.
Another alternative for this experiment that would not need a spectrophotometer would be a 2-container apparatus using quartz glass that is transparent to UV (especially the 300-380 nm range). You would have one container on top of the other with sunlight shining from above (so the sides of the containers should be made opaque to only have light come from above). The one on top would contain CYA or CYA+FC and you should also have a control with just water. The bottom one would contain FC with no CYA and would be used to "measure" the rate of chlorine degradation. We know that with no CYA that chlorine degrades rapidly from the UV in sunlight. The bottom container should have the pH high so that the chlorine is mostly hypochlorite (you'd need a pH meter or an extended or high-range pH test for this). A pH of 9.0 would have 97% of the FC be hypochlorite ion and that has a half-life in direct noontime sun of only 20 minutes in shallow depths (but using a control under the same conditions would let you calculate relative protection so UV absorption).
it might be interesting to examine the conditions whereby 0 FC actually converts CYA into ammonia.
The main controversy with this is that some claim that the bacteria will only grow in anaerobic conditions and that pool water is not sufficiently anaerobic. So if you can take regular pool water exposed to air with modest circulation and can have bacteria grow in it and convert CYA into ammonia or just degrade the CYA in general, then that would be interesting. To encourage bacterial growth, you'll want to add nutrients to the pool so fertilizer (phosphates and nitrates) though that will also support algae growth so you can keep the water in the dark which should limit algae growth but still allow bacteria to grow. You can take some soil to add to the water and you'll want the water to be warmer to speed up the experiment (around body temperature is ideal but 90-95ºF would be OK). Unfortunately, this experiment is likely to fail most of the time since the conversion doesn't usually happen.
1) Manipulate TA & CH & pH to get various CSI levels and see if scale forms as predicted.
2) See how quickly some copper pipes dissolve at various low pH levels.
One can over-saturate the water with calcium carbonate and not see scale, but if one introduces nucleation sites then the precipitation can occur more rapidly. So having some solid calcium carbonate already in the water can then be weighed even if you don't see cloudiness or additional precipitation. Or you can use a plaster coupon but that's more complicated to make.
For copper corrosion you want a container with water that is not only controlled in pH (you can use phosphate buffers for that) but that has water flow. Measuring corrosion can be tricky but you can use a scale that measures 0.01 g up to 500 g (such as
this one and get a 500 g standard weight such as
this one). It won't distinguish between the copper oxide layer, but it should measure any copper losses and you could use a copper test to measure copper ion ppm in the water as well. You can also repeat the experiment using high chlorine levels and even combine the two for a matrix of chlorine and pH levels.
How about constructing a simple SWG cell and predict and analyze the ion chemistry involved?
A variant of this would look at the differing amounts of chlorine vs. oxygen gas that are produced as a function of the chloride salt level (one can use potassium sulfate or other non-chloride salt for equivalent conductivity at zero to low chloride levels) and as a function of different electrode materials used such as carbon vs. different non-electrolyzing metals (platinum is expensive, however) and both uncoated titanium and titanium coated with ruthenium, but the latter can be expensive or hard to find.
