Solute particles jump around when tub is draining

[KatieWoe]

Test device:
Dell
Operating System:
Win 10
Browser:
Chrome
Problem description:
Minor bug found in phetsims/qa#309.
When there are a smaller number of particles sitting at the bottom of a saturated solution, draining the solution causes some of the particles to move along the bottom wildly until draining stops. Seen in older versions, so not connected to the above release.
Steps to reproduce:

1. Select a solute and add it until you have a saturated solution with particles on the bottom
2. If there are too many particles, use the dropper to dilute it until you have a smaller number
3. Drain some of the solution and watch the particle behavior

Screenshots:

Troubleshooting information (do not edit):

Name: ‪Concentration‬
URL: https://phet.colorado.edu/sims/html/concentration/latest/concentration_en.html
Version: 1.3.13 2019-04-22 08:50:58 UTC
Features missing: touch
Flags: pixelRatioScaling
User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/73.0.3683.103 Safari/537.36
Language: en-US
Window: 1536x722
Pixel Ratio: 2.5/1
WebGL: WebGL 1.0 (OpenGL ES 2.0 Chromium)
GLSL: WebGL GLSL ES 1.0 (OpenGL ES GLSL ES 1.0 Chromium)
Vendor: WebKit (WebKit WebGL)
Vertex: attribs: 16 varying: 30 uniform: 4096
Texture: size: 16384 imageUnits: 16 (vertex: 16, combined: 32)
Max viewport: 16384x16384
OES_texture_float: true
Dependencies JSON: {"assert":{"sha":"7d27130a","branch":"HEAD"},"axon":{"sha":"9bf8f88c","branch":"HEAD"},"babel":{"sha":"735d57d7","branch":"master"},"beers-law-lab":{"sha":"10281f45","branch":"HEAD"},"brand":{"sha":"b040cac5","branch":"HEAD"},"chipper":{"sha":"0ebc6913","branch":"HEAD"},"concentration":{"sha":"b4e5af61","branch":"HEAD"},"dot":{"sha":"04efe0bc","branch":"HEAD"},"joist":{"sha":"a9ad0567","branch":"HEAD"},"kite":{"sha":"dce9765e","branch":"HEAD"},"nitroglycerin":{"sha":"ad3cb990","branch":"HEAD"},"phet-core":{"sha":"c48bf320","branch":"HEAD"},"phetcommon":{"sha":"3a85ef86","branch":"HEAD"},"phetmarks":{"sha":"3fdfece0","branch":"HEAD"},"scenery":{"sha":"864e3a56","branch":"HEAD"},"scenery-phet":{"sha":"2b60b8e4","branch":"HEAD"},"sherpa":{"sha":"e90b735f","branch":"HEAD"},"sun":{"sha":"6f66368f","branch":"HEAD"},"tandem":{"sha":"29f64233","branch":"HEAD"}}

[pixelzoom]

Transferring this issue from concentration to beers-law-lab repo, since the former is a subset of the latter.

[pixelzoom]

This is a duplicate of #175. We thought that issue had mysteriously corrected itself, but apparently not. I'm going to move the info in #238 (comment) to #175, and close this as a duplicate.