View Full Version : Need help with ATO water dosing

01/02/2011, 09:37 AM
I run a 5 gallon bucket of RO water and a small powerhead to supply ATO water to the tank. My water comes out of the RO system at 0.9-1 dKH and 0 ppm calcium.

I had been pre-dosing the water to a dKH of around 8.8 and a calcium level of around 450ppm using Dr. Holmes-Farley's 2-part recipe #1.

I've been having an unexplained alk drop to around 7-7.4 dKH and my calcium has hit around 490ppm using this method of pre-dosing the ATO water. How does one determine how or to what level is the appropriate pre-dose of the ATO water? Assistance is appreciated.



01/02/2011, 09:53 AM
When your tank salt water evaporates the salts remain in the water and only the H20 leaves the tank. So you don't add alk and calcium at the same amount as found in your tank. You dose alk and calcium per the consumption rate of your tank occupants and perhaps some lost precipitation. ;)

When you mix both alk and calcium supplements in your rodi water this will lead to precipitation of calcium carbonate. This means you will get a very large drop in alk compared to calcium when the precipitants form in your rodi water for top-off. You only want to add either alk supplement or calcium supplement, not both. Adding alk supplement to your rodi water top-off makes most sense because alk is used much quicker in a reef tank.

Bottom line is you need to calculate your weekly alk consumption of your tank and add the appropriate amount to your top off depending on your evaporation rate. The calcium part will have to be dosed separately. ;)

01/02/2011, 10:22 AM
Hopefully you put your dosing pump on a timer in case your float sticks which would lead to dumping 5 gallons of rodi water in your tank at one time, which can cause problems. ;)

01/02/2011, 12:17 PM
Spot on with both recommendations.


01/02/2011, 03:12 PM
Pumo is on a timer and uses a relay outlet with my Apex so it won't hang in the ON position. Thanks for the info - will dose the alk in the RO and dose the calcium like 1-2 times a week. Load is light right now.


01/02/2011, 03:15 PM
Your welcome. ;)

Sounds good to me.

01/03/2011, 06:37 PM
Just to make sure I'm doing this right, I'm losing about .4 dKH per day. I have to add 28ml of Randy's Recipe #1 to 5 gallons of ATO water to get the alk from around 1 to 9 dKH.

I'm losing about a gallon or so of water a day, and the timer, running the pump for 45 secs, puts 1 gallon of water into the sump.

To raise the dKH in my tank (system volume 115 gallons), I have to add 32 ml of alk to the tank daily to keep the alk at around 9 dKH. So, do I dose the 5 gallons of ATO water to a baseline of 9 dKH, and then add 150 ml (30 ml X 5 gallons) to the ATO reservoir to maintain the alk level on a daily basis?

Please advise. Really don't want to screw this up.


01/03/2011, 09:34 PM
You do not need to care what the level of alk in the topoff water is. If you tank uses 32ml of recipe 1 a day, and it takes 5 days to use your topoff container you would put 5 days worth of alk doses into the water. That would be 150ml. Whatever the water turns out to be alk wise does not matter. The 1 gallon of topoff water with the 30ml of alk solution makes it into the tank daily which will make up for the consumption of alk in the tank. If you predose to raise the alk to 9 in the topoff container and then add 30ml for each day you will be slowly raising your main tank alk levels.