Something Fishy Is Going On Here...

[Colin_T]

if your PH is dropping due to lack of surface turbulence you could have too much carbon dioxide (CO2) in the tank. That would kill the shrimp without any signs, especially overnight. During the day the corals and algae would photosynthesise and produce oxygen but at night when the lights were off, everything in the tank would be using oxygen. This includes things like live-rock, corals, fish, starfish and marine plants/ algae.
It could be the creatures have been suffocating, too much CO2 and not enough oxygen.

 

[SkiFletch]

Possible indeed. Just goes to show you how important surface agitation is. That's a significant rise just from increasing surface agitation

 

[n3ont3tra]

Yeah but the powerhead was still pointing at the surface when the shrimp died. It only got moved on Friday.

 

[Colin_T]

I think it is probably the low PH and maybe fluctuating PH.
Do some water changes and keep the PH up and see how things go over the next month. If nothing else dies then hopefully that will be that.

What is the temperature of the tank and is the thermometer reading correctly? Maybe take your thermometer down to the LFS and compare the reading to a few of theirs.
If it is a faulty thermometer the water temperature could be too high and cooking the inverts. Also the warmer water will hold less oxygen.

 

[n3ont3tra]

I keep it at 82 because I can keep it at 82 all day in the summer easily. It doesn't fluctuate at all. I've tested it against two thermometers.

 

[Colin_T]

ok, no worries.

 

[n3ont3tra]

Got teh TDS meter.
tap water: 115ppm
RODI: 63ppm

I've been using some RODI water from my mom's work for topoff for the last week, it just tested at 1ppm.
The TDS meter was calibrated to 800ppm.

So maybe the RODI is the problem.

 

[SkiFletch]

Ding ding ding, we have a winner. 63ppm indicates a membrane which either needs flushing or has fully failed. Do you have a flush kit installed?

 

[n3ont3tra]

Nope....

 

[littleme1969]

Flush kit for an RO.. watches for response with bated breath as I need to instal one too

 

[Colin_T]

you've changed your appearance littleme1969
It looks good

 

[n3ont3tra]

I just checked with my mom, the water she is getting is milli-q. Is it safe to use for now?

 

[SkiFletch]

If it's TDS is that low, go right ahead and use it....

And you can buy flush kits here in the States. I'm sure they could be purchased in the UK from Osmotics, RO Man, or something similar

 

[n3ont3tra]

How often are you supposed to actually change the membranes?

 

[SkiFletch]

Well, you need to change them when flushing them no longer rejuvinates them... Different for everyone's membrane. My own membrane is 3 years old but it still works great. I flush for 10 mins before every time I use it and my water is always 1-2ppm TDS. Clearly no need for me to replace it yet . So if I were you, I'd get a flush kit, try flushing it, and see if it recovers. If so, keep using it, if not, time for a new one. Either way, flush religiously, it really helps prolong membrane life for sure.