To date I've tested the following electrolytes.
- Potassium Hydroxide (KOH)
- Sodium Hydroxide (NaOH)
- Vinegar(CH3COOH)
- CLR (Calcium, Lime & Rust Cleaner, proprietary mix)
- Baking Soda (NaHCO3)
- Baking Soda/Vinegar (NaHCO3/CH3COOH)
- Magnesium Sulfate (MgSO4·7H2O)
- Sea Salt/Sodium Silicate (NaCl)
- Calcium Hydroxide (CaOH)
- Ferrous Sulfate (FeSO4·H2O)
- Borax (Na2B4O7·10H2O)
- Kool-Aid (Citric Acid, Ascorbic Acid, others)
I note that for the purposes of this test, there were three classifications of effect and two that I recorded. Particulate is the formation of solids in the electrolyte, usually brown. Particulate usually settles on the bottom after testing with the exception of vinegar. Scum is the formation of a surface viscus mass that interferes with bubbles bursting. Scum does not seem to have a color of it's own and usually dissolves back into the water within a few minutes of electrolysis. Foam is similar to scum in the interference of bubble bursting, but without direct observation of a substance on the surface. Foam usually lingers on the surface for awhile after electrolysis. Foam measurements were not taken, but foam formation did cause me to abort the CLR test.
I determined early on that using distilled water or reverse osmosis purified water has by far the least effect on particulate formation. This in turn causes me to assert that ordinary tap water with high mineral content should be avoided when performing electrolysis. Softened water is also better than plain tap water, but is still second to distilled or reverse osmosis purified water.
Despite some inconsistencies in the tests these are the results. I may add tests to this series but felt there was enough of a body of work to produce a summary.

I also note that compounds containing Magnesium or Calcium should be avoided as they leave hard water deposits on the container and plates.
NOTE: Wear hearing protection when igniting a foam buildup!!! Igniting foam makes a sound at least as loud as a high caliber rifle or shotgun.