Question about dosing by PH in Hydros

BambooKing · Sep 17, 2025

Hi all,
I apologize about this being my first post, but I have not gotten around to posting my build thread. I have a question about a situation that I am facing with my tank. I have a hydros X10 and xp8 that I am using on my tank and I set it up to dose (from my Avast k2) in my IM112. I set up the hydros to dose kalk from a BRS 5ml dosing pump to the stirrer whenever the ph drops below 8.2 and stop when the ph gets above 8.3. It has been working brilliantly. The other morning though, I turned off the lights so I could introduce a couple new fish. I noticed the BRS 5ml dosing pump turning on and off quite a bit. I thought it was because the lights were out and it was trying to keep the ph above 8.2(it probably was). The problem was my sump was actually filling up beyond where I am comfortable. I don't have a water level detector on the sump(I have since ordered one) but I am sure it would have gone far past it. My hydros ATO had not run in two days. I started to think about what would happen if my kalk stirrer has not producing a saturated enough solution to keep up with the minimum ph of 8.2? I looked at my kalk stirrer, and it looks like it has 4-5" of kalk at the bottom but the top 4" is clear and not milky. I have to admit that when I first filled it up about 3 months ago, I put 4 cups of kalk in it(maximum suggested dose)!! It even caused the stirrer motor to strain as it stirred. That has recently stopped. My first question, is do we suspect that the kalk somehow precipitated and even though the stirrer shows 5" of kalk at the bottom, the solution is quite weak?(tested it with a stick device at 6.09ms/c). Also, is my method of dosing the kalk flawed in that if it can never meet the 8.2ph then it will dose my entire 10 gallon Reef Can of RO into my rather small sump, thus flooding my tank? Other culprits could be my AWC which consists of a double headed sterner pump which seems to be pumping in and discharging out flawlessly. Any suggestions, questions, accusations??? Thank you.

Randy Holmes-Farley · Sep 17, 2025

Dosing anything by pH risks excessive alk, and in fact, will more often than not in low pH situations reach excessive alk before the pH target is attained.

Ryans Reef · Sep 17, 2025

I have the IM112 as well. Such a nice tank.

If I understand your set up correctly then yes, it's not an ideal way to run your tank for several reasons:

Dosing kalk based off pH does run the risk of overflowing your tank if your pH set point isn't reached, and there's no safeguard sensors in place. pH probes need to be recalibrated often as their accuracy shifts. Stable salinity would be more important that rock solid 8.2 pH as well. Also, by focusing only on pH and presumably not on your alkalinity, you could end up with substantially high alk. And as your kalk reactor runs the potency of it will decrease over time meaning you will be dosing more of the solution than normal, thereby lowering your salinity.

You may already know this, but pH is a unique parameter. It's a logarithmic scale of the acidity of the water. It changes throughout the day due to a variety of natural causes. As such you shouldn't treat it as other tested values such as Calcium or Magnesium.

For example if you do a Calcium test, and you get 425ppm, that's a value of 425 parts Calcium per million of your tested solution. pH is not a value like that. You don't have 8.2 parts per million of pH in a tank. It's a measure of how acidic your water is. And that shifts throughout the day due to photosynthesis, organic activity, etc. As a result I find it far too risky to dose based off pH.

Instead I would recommend dosing based off of alkalinity, while also trying to maintain your pH within a set range. Try to stabilize pH in your desired range by dosing kalk (within the limits of the alk range), opening windows, using a skimmer, increasing surface agitation, using CO2 scrubbers etc.

For some further reading:

Understanding pH in Reef Tanks: Part One

Few parameters in reefkeeping cause as much disagreement as pH. Some consider managing it, let alone testing it, unnecessary or even potentially harmful. While pH usually falls into an acceptable range in most tanks, it can be borderline low in others, causing stress and the risk of dissolving...

www.reef2reef.com