Salinity plummeted over night - any thoughts on why?

[JohnH123]

Hi Everyone,

Just wondered if anyone could throw any light on why my salinity plummeted overnight?

I've got a 300lt tank with a 50lt sump FOWLR. Salinity has been stable at 1.024 for ages - years in fact.

The other night I was watching a film and suddenly heard the pump go very noisy. Opened the doors to the sump to see my auto RO top up system had blocked and the partition in the sump with the pump in was below the pump inlet. I'm pretty certain I caught it within minutes of it being a problem. I turned off the pump, gave the filters under the sink a good bang and the RO started to fill the sump again. I turned off the pump and the protein skimmer and UV filter whilst the water level rose high enough. The protein skimmer was full but was virtually pure salt water with no discolouration so I let that empty back into the sump. There was a heater in the pump section on the sump and that had over heated due to being above the water level and gone bang.

When the water was high enough, an hour or so later, I turned the pump back on.

I thought I'll deal with the heater in the morning.

In the morning the banded shrimp was dead but the fish were ok. I wondered if the salinity was ok and checked it. It can't have been more than 1.005, the salinity had virtually gone.

There are no leaks visible and nearly all the water would have had to empty out of the tank and be replaced by the RO top up system to drop the salinity by that much.

Can anyone see anything in my description that could have caused the salinity to plummet?

Many thanks in advance everyone.

John

 

[windemerejack]

faulty meter?

 

[Holst]

Any other visual signs on corals, fish and inverts? Beside the one dead shrimp
sounds more like misreading..

 

[JohnH123]

Hi Guys,

The banded coral shrimp died. I took some water out of the tank and added salt to it to check the refractometer. It seems to be working fine. I'm adding salt into the sump daily. I know people recommend adding salt water to top up but thought the salinity was so low it required immediate intervention. Salinity is climbing.

 

[Holst]

Hi Guys,

The banded coral shrimp died. I took some water out of the tank and added salt to it to check the refractometer. It seems to be working fine. I'm adding salt into the sump daily. I know people recommend adding salt water to top up but thought the salinity was so low it required immediate intervention. Salinity is climbing.

Have a reefer near you so you can compare readings or do you have Refractor calibration drops? Think you need to have at least one KNOWN factor.. and until your sure you are Reading correct you dont have that..

 

[Garf]

Hi Guys,

The banded coral shrimp died. I took some water out of the tank and added salt to it to check the refractometer. It seems to be working fine. I'm adding salt into the sump daily. I know people recommend adding salt water to top up but thought the salinity was so low it required immediate intervention. Salinity is climbing.

Is the top off connected directly to your RODI unit?

 

[windemerejack]

are you sure the shrimp is dead and not just moulted?

 

[Duncan62]

Have a reefer near you so you can compare readings or do you have Refractor calibration drops? Think you need to have at least one KNOWN factor.. and until your sure you are Reading correct you dont have that..

Get a simple hydrometer. It isn't as precision as the modern test methods but it is always the same. Specific gravity of the water a a constant temp should be constant. Good low tech check for all these things that require calibration. Keep one floating in the sump and you get a very good idea of salinity at a glance.

 

[lavoisier]

When I have had salinity drops in the past it was usually because my skimmer (for whatever reason) needed adjusting as it was draining tank water from the system which was being replaced by fresh water from the top off tank.

 

[JohnH123]

Hi Everyone,

Thanks for all your replies and suggestions. I bought the tank second-hand a few years ago and the chap I bought it off chucked in a few bits and bobs he didn't need anymore, amongst which was a refractometer. Both my expensive and his cheaper refractometer are giving the same readings. I'm adding about 500g of salt per day and the salinity now reads about 1.016 on both.

Yes, the top up RO runs with a small ballcock and runs straight out of the RO filters under the sink. I've ordered some new filters for it.

It seems very peculiar that the this happened after the RO system blocked and let the pump section of the sump run low, but as I said, I think I caught it really quickly.

The skimmer was full but if it was actually emptying the tank the water has nowhere to hide and would be coming out from under the tank all over the floor.

The only other factor that I deliberately didn't mention to begin with because I wanted to see if someone said, "this is what's happened."

I doubt it's the case, but a couple of month's ago I finished with a girl who does have a key to the place. Is there anything anyone could throw in that would neutralise the salinity?

Thanks,

John