My float switch stuck and this is what happened....

DRC Archive General Saltwater Discussion
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I have a DIY ATO that Shawn built for me on my 39g frag tank and it has worked flawlessly since I installed it. In fact, even though one of the float switches stuck last night it still worked just as it should have because the second switch kept my tank from overflowing. The only problem is I use kalk in my ato and before the water level reached the second switch about 2 gallons of water was dumped into my tank. Of course this was only a couple of hours after I refilled the top off container with fresh RODI and kalk.

I knew something was terribly wrong when I walked downstairs and the tank look like a vanilla shake. I couldn’t see 1/4" into the tank. My Ph shot up from 8.3 to 9.1. This was around midnight and I was tired and trying to think through how I should handle this without overreacting and making the situation worse. I considered changing out 25-50% of the water, but thought this might cause more precipitation stressing the already stressed corals more. I then considered adding some vinegar to bring down the Ph, but worried that might cause more stress also. In the end I decided to do nothing and let the tank settle on its own. I really could not tell how the corals or two fish were doing because I couldn’t see them, it was that milky.

When I got up this morning at 6 am the tank had cleared and the Ph was sitting at 8.38. Everything looked just fine and tonight things still look just fine. The only coral that has shown any reaction at all is a small 1/2" frag of orange cap. It look pale and is looking like it may bleach. I ran some quick tests and my dkh is down to 6 from 8, and the calc is down to 360 from 400. I will slowly get these numbers back where they should be over the next few days. I think I made the right decision, but only time will tell if any of the more sensitive sps have a delayed reaction. I plan on shortening the distance between the two switches so that if this happens again less water will be added to my system. Just thought I would share this experience in case it ever happens to anyone else in the future.

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You are lucky, Sorta, i think. a Kalk dump, although high in PH is low in density. Which is why kalk alone cant keep up with high calcium demand dense SPS tanks. a dark tank, in night time respiration mode, can consume much of the alk/ph dump over night by producing CO2 and carbonic acid to nutralize the high PH. which is why we all drip 12.5 PH kalwasser at night. to reduce the night time low PH swing. I bet the Orange Monty Cap may recover. if not, i can make a frag for you.

sounds like The ATO safety system save a catostrophic dump.

That’s guuud!!

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Ellen, its great you didn’t have any long term affects beyond possibly your monti. I also have a DIY Shawn ATO, and although, I don’t drip kalk with it, I was concerned about the backup float being 1"+ directly over top of the primary float. The primary float, since its mostly underwater is certainly susceptible to gathering growth, or snails, etc. Since I needed to adjust the height of the floats anyway, I used a wider piece of plexi to glue the two floats staggered about a 1/2" apart (up and down) and side-to-side (next to eachother). That way, I figure I have a significantly less chance of overdosing straight RODI if the primary float fails and the secondary one has to come into play.