Water change + top off all in one

[iaa12]

Have a RedSea Reefer 350, 91 gallons total. Currently topping off automatically with a Hydor ATO from a 50 gallon bucket of RO/DI, working out great. I got to thinking, I'd like to make life easier on water changes as well.

I'm currently evaporating about 2.5 to 3 gallons per week, and I'd like to do a 5 gallon water change every week.

It takes approximately 2.5 cups of RedSea salt to make 5 gallons of saltwater. If I added 2.5 cups of salt (I'll measure it exactly in grams but go along with me here) for every 8 gallons of top off water(5 change+3 evap), then I'd be adding 0.9 cups of salt (3/8*2.5) during the week as I make up for evaporation, slightly increasing salinity. Then over the weekend, I can simply take out a 5 gallon bucket of water from the sump, the ATO kicks in, and replenishes the 5 gallons - reducing salinity back to its target value in the process. Obviously monitoring of salinity and dialing in of salt quantity would be required, and the weekly 5 gal water change would be required to keep it in check.

Question - would that be too much of a salinity swing every week, 1 cup of salt for 90 gallons volume in either direction? Am I missing anything important?

 

[killer2001]

Sounds like you need to invest in a daily AWC system. Ditch the 5 gallons every week idea and go 1 gallon a day AWC.

 

[iaa12]

Sounds like you need to invest in a daily AWC system. Ditch the 5 gallons every week idea and go 1 gallon a day AWC.

I've considered it, but besides the $$$ for the controller, sounds like in addition to my current reservoir of fresh water I would need another reservoir of salt water, and yet another reservoir for the water being drained from the tank. I'd like to avoid all those buckets if at all possible.

 

[Randy Holmes-Farley Verified Community Expert]

It is fine to combine water changes and top off, but waiting a week for top off sounds too long to me.

3 gallons in 91 gallons total will allow the salinity to slowly swing from 35 ppt up to 36.2 ppt, then instantly back down again on water change.

 

[iaa12]

It is fine to combine water changes and top off, but waiting a week for top off sounds too long to me.

3 gallons in 91 gallons total will allow the salinity to slowly swing from 35 ppt up to 36.2 ppt, then instantly back down again on water change.

Great, thank you. I do not plan on waiting a week to top off, I will be topping off constantly with the dilute saltwater mentioned, via ATO. My current plan is to do a 2 gallon water change every 2 days when I swap out the filter floss. I have a 2 gallon bucket, a pump already in the sump, should be a 1 minute job. This should greatly reduce any salinity swings as well.

I wanted to ask a couple of followup questions:

- Is there any relation between the water salinity and its capacity to carry calcium, magnesium and carbonate alkalinity? Since the top off water will only have 65% of the salt mix added, it will also be low on calcium, magnesium and alkalinity. I'd like to bring the top off mix to 450ppm Ca/9dkh/1450ppm Mg via additives, to equalize it with the tank. I was wondering if/how the low salinity will impact my ability to do so - in either direction.

- Related to above - should my Ca/Mg/CO3 consumption increase in the future, what is the maximum carrying capacity of saltwater until precipitation occurs? Could I beef up the top off water to 600ppm Ca, 14 dKH, 1600 Mg? Wondering if this could also replace dosing.

 

[Randy Holmes-Farley Verified Community Expert]

- Is there any relation between the water salinity and its capacity to carry calcium, magnesium and carbonate alkalinity? Since the top off water will only have 65% of the salt mix added, it will also be low on calcium, magnesium and alkalinity. I'd like to bring the top off mix to 450ppm Ca/9dkh/1450ppm Mg via additives, to equalize it with the tank. I was wondering if/how the low salinity will impact my ability to do so - in either direction.

Yes, normal salinity seawater can hold calcium and alkalinity at 450 ppm and 9 dKH better than lower salinity seawater. magnesium is a part of that, but not the only part.

- Related to above - should my Ca/Mg/CO3 consumption increase in the future, what is the maximum carrying capacity of saltwater until precipitation occurs? Could I beef up the top off water to 600ppm Ca, 14 dKH, 1600 Mg? Wondering if this could also replace dosing.

Raw salt water is very prone to precipitation of calcium carbonate since it has fewer materials that prevent it (such as organics, bacteria, phosphate, etc.).

Red Sea coral pro (12 dKH and elevated calcium and magnesium) is known by the manufacturer and some users to have such issues, and I would not recommend pushing things higher than that.

 

[iaa12]

Alright, the plan is in motion. I made a full 44 gallon Brute trash can worth of top off water, using
~13 cups of Red Sea Coral Pro salt (instead of 22 normal). This resulted in water with 1.016 specific gravity, 5.7 dKH, 270 ppm calcium, 840 Magnesium. I adjusted to 9.7 dKH using 4 teaspoons of Seachem Reef Builder, 440ppm calcium using 20 teaspoons calcium chloride, 1350ppm magnesium using 850 grams magnesium sulfate heptahydrate.

The ATO has been topping off with this water for the last 36 hours so I removed 2 gallons of tank water from the sump today - ATO kicked in and refilled, everything worked as planned, salinity looks good. So far so good, I'll continue doing 2 gallon water changes every other day as I change the filter floss, keep an eye on tank salinity - if it increases too much I'll do an extra water change, if it's low, I'll skip a water change. As well as monitor Ca/Alk/Mg. I'll report back with findings in a few weeks.

 

[Randy Holmes-Farley Verified Community Expert]

Alright, the plan is in motion. I made a full 44 gallon Brute trash can worth of top off water, using
~13 cups of Red Sea Coral Pro salt (instead of 22 normal). This resulted in water with 1.016 specific gravity, 5.7 dKH, 270 ppm calcium, 840 Magnesium. I adjusted to 9.7 dKH using 4 teaspoons of Seachem Reef Builder, 440ppm calcium using 20 teaspoons calcium chloride, 1350ppm magnesium using 850 grams magnesium sulfate heptahydrate.

The ATO has been topping off with this water for the last 36 hours so I removed 2 gallons of tank water from the sump today - ATO kicked in and refilled, everything worked as planned, salinity looks good. So far so good, I'll continue doing 2 gallon water changes every other day as I change the filter floss, keep an eye on tank salinity - if it increases too much I'll do an extra water change, if it's low, I'll skip a water change. As well as monitor Ca/Alk/Mg. I'll report back with findings in a few weeks.

Sounds good!