Sudden spike in pH due to initial soda ash dosing in auto-fill?

[MnFish1]

There is nothing wrong with using soda ash! My pH runs about 7.8 using baking soda. So I use soda ash and a very slow 24/7 drip that keeps my pH right around 8.0.

But if your pH is already in an acceptable range, why use soda ash and drive it up even higher?

Agreed - but in this case - I think the problem is that here ATO dumped all of it in at once. Its why you have to be careful with the Red Sea Reefer ATO and using kalk for example. If for some reason ( and I did it once) you take the water level down (like a quick cleaning, etc) - if the ATO valve (which is gravity fed) is full open - it will quickly dump a bunch of alkalinity solution into the sump/tank. If its set (as its supposed to be) to drip every second or so (and turned off when the water is too low due to extraneous circumstances) this spike can't happen.

My guess is that the tech emptied too much water during the 'water change' - when the alkalinity was put into the ATO - it just filled back up with that water - resulting in the spike. The Tech should have added more water such that the ATO would only replace due to evaporation. Its either that -OR- the ATO float valve on the RSR has failed (which btw has happened to both of mine (I no longer use them). There is no other way to explain these results

 

[MnFish1]

I'm a little confused, but that is extremely easy to do.

I have to believe that what you're terming "auto fill tank" is your Automatic Top Off (ATO) reservoir. This will automatically add relatively small volumes of RO/DI water to your tank/sump to replace water that has evaporated. These volumes tend to be fairly small, and many over the course of a day, and would have minimal impact on pH. Therefore, I've got to believe you have your pH probe in this ATO reservoir....which also doesn't make sense, because pure RO/DI water is not going to have a pH of 8 or so.

Four tablespoons of Soda Ash (Sodium Carbonate) in approximately 2.5 gallons of RO/DI water is not that much alk solution. Dr. Randy's DIY formula for his standard alk solution is 2 cups made up to one gallon.

This is a head scratcher for me, because it just doesn't make sense. Something is not right.

With the Red Sea Reefer - there is a reservoir that is gravity fed to a float switch near the pump. You can manage the flow through that tube (via the valve shown in the picture). If the level is lower by evaporation - the alkalinity slowly drips in. You need to make sure the valve is set such that if someone (like the tech that did the water change) accidentally doesn't put enough water into the sump - that the water from the ATO only slowly drips into the tank. I have two of these tanks - and have experienced the same thing first hand. If you forget to shut off the ATO during maintenance and are using KALK for example - you will get 500cc of Kalkwasser rapidly into the tank. So - the maintenance person needs to be sure that the water where the float valve is - is completely full (again sorry to repeat) - my guess is that the tech did not do this. When she added the Alkalinity to the ATO it rapidly went into the tank - because the valve was too 'open' (its manually set) and the tech didnt replace enough water with the water change.