I experienced this with an older rpi using a USB wifi dongle, and more recently with rpi 3. In my case, it seemed to be a power related problem. The wifi modules weren't able to pull enough power to stay connected to the weak wifi signal. I upgraded my power supply and no longer experience that issue.
Connecting directly to ground is fine. The 10k pull down is only required if you might use a jumper to connect to 5v.
That's fine. I don't expect that to be an issue. It's essentially the same thing that happens on the breakout board when you bridge an address pin.
Process: 750 ExecStart=/usr/bin/reef-pi daemon -config /etc/reef-pi/config.yml (code=exited, status=1/FAILURE)
I went from 2.2 to 2.5 and had some minor problems with my pca (leds didnt turn off). I found that 2.3 works best for me. Not sure if it is relevant to you though.
journalctl -u reef-pi.serviceThats awesomeOne is really a diy freak when you start to pick up random stuff off the street and think "Hmmm.. this connector looks interesting, wonder if I can use it in a reef-pi build..?"
I found a badly crushed run over controller for an ebike in the street the other day. The connectors looked interesting and I thought maybe I could save something from it so I took it home and did an autopsy. I saved a heatsink for 7 mosfets but otherwise no electronic parts. But the connectors looked really interesting, waterproof with a lot of pins. Sadly I only had female connectors.
I started to google the brand name I saw on one of them (Julet) and found a big world of ebike connectors opening up to me. IP67 connectors with up to 10 pins in a quite small form factor. For both signal and power. I haven't found a source for these connectors though, many seem to be OEM connectors not available for consumers but there seems to be a diy scene in the ebike community so all hope is not lost.
The one I'm holding in my hand has 6 pins. The larger two on the table has 10 pins. Everything is IP67 by the looks of it. Nothing is chassi mounted though, only in line (right term?).
I thought it was interesting and potentially useful if there are spare connectors available for a decent price. I'll keep looking. If anyone knows anything more please let me know!
. Nothing like scavenging electronics and reuse. During the 2.0 to 3.0 upgrade process I realized I rarely need to buy any new electronics, as pretty much everything except the enclosure and may be some perma proto board is reusable . It turned out lot less expensive than I was anticipating. 
Ack. Let me test it out with 1500 frequency settings.
journalctl:
Oct 27 14:18:00 ReefControlPi systemd[1]: Started raspberry pi based reef tank controller.
Oct 27 14:18:00 ReefControlPi reef-pi[311]: 2019/10/27 14:18:00 Setting pca9685 frquency: 1500
Oct 27 14:18:00 ReefControlPi reef-pi[311]: 2019/10/27 14:18:00 ERROR: Failed to initialize pca9685 driver with mock i2c bus.
Oct 27 14:18:00 ReefControlPi reef-pi[311]: 2019/10/27 14:18:00 ERROR: Failed to initialize controller. Error:remote I/O erro
Oct 27 14:18:00 ReefControlPi systemd[1]: reef-pi.service: Main process exited, code=exited, status=1/FAILURE
Oct 27 14:18:00 ReefControlPi systemd[1]: reef-pi.service: Failed with result 'exit-code'.I dont think that's the issue. I've downgraded to 2.3 and the issue is the same. It looks like the problem is coming from upgrading to the latest version of rasbian (Raspbian GNU/Linux 10 - buster) or some related module upgrades. This same 2.3 setup was working on Stretch Lite for almost a year, now with Buster + 2.3 it fails.
www.reef2reef.com
reef-pi :: An opensource reef tank controller based on Raspberry Pi.
It is the web browser. Clearing cache and local storage in the browser for the reef-pi website may solve it. I think I had suggested these. Like hard refresh or access reef-pi ui from incognito mode
Looks Like version 2.x does not support an other adress then 0x40, maybe better to move to 3.0
