Impact of DSB refugium on water changes

[honeypotGlen]

I've been searching for a discussion about this, but no luck.

I am adding a sump/refugium with a dsb to my 75 gal. I have seen posts where people say the water change amount is calculated as a percent of the total water volume of the system (display tank plus sump/fuge), but I don't understand the logic to this. Assuming the bioload is the same, consider...

1. The fuge is removing some of the nitrates, so the water should get contaminated at a slower rate.
2. There is more water in the system, so the waste is diluted more.

I would think that at the MOST the water changes would continue at the same rate based on the volume of the display tank. More likely, I would think that the assistance of the dsb would reduce the amount of water change needed. What do people here think about this? How is water change volume and frequency calculated when adding a dsb fuge?

 

[PasstheTorch]

imethe % that people change is based on how much water is in their system. so if i had a 100 gallon tank and added a 50 gallon fuge, my total water volume is 150 gallons. i do 10 % water changes so i would do 15 gallons. waterchanges should not effect the sand at all becase your not touching it. you just taking water out of the tank from the surface. ift its a deep live sand bed, dont tough it.

 

[honeypotGlen]

jlax - I think that makes sense if we assume the same bioload is spread out over more gallons. Doing it your way would remove the same amount of waste. But, if the dsb refugium is processing some waste out, shouldn't we expect the percent of system water changed to go down some?

 

[Jocko]

I think part of the problem here is that there is no standard for water change % and frequency. So unfortunately this discussion starts off with a moving target.

I guess water changes are supposed to help with replacing trace elements. Personally for me I think the biggest thing is removal of dissolved organics. So a part of deciding how much you want to change water is based on that. And the buildup of DO is going to vary based on a number of things both for input and output. I.E. do you feed a lot or a little. Do you run carbon? What kind of skimmer do you have?

And I guess the biggest problem is that we can't measure the DO! So how do you even know you're doing it right? This makes it a more of a long-term process based on qualitative observations. Nuisance algae growth. Coral health. Etc. It will take a long time to figure out if you're spot on. Of course you can always err on the side of doing excessive water changes. And including the sump volume is a good step in that direction.

Actually it just occurred to me that sumps are a great place for detritus to settle. So they may in fact contribute more that you might think unless you clean that out regularly.

 

[SteveDola]

so you want to do smaller waterchanges because you have a larger DSB+water volume?
Adding 50g of water + more DSb will dilute the biowaste and make waterchanges even that less effective for waste removal. The DSB will add to your overall biofiltration but to replenish trace elements you will need to replace a good percentage of water.

I personally dont do large water changes but rather do smaller waterchanges every week to help maintain a consistant level in my tank. Seeing that you have that added 50g of volume you could prolly do 10g changes weekly rather than 15g. But thats based on you have a good skimmer and plenty of LR to help get rid of that waste.

 

[Reef_Wizard]

IMO, % of total volume (a fixed volume - with or without DSB) is not a good way to measure water change needed. It is a starting point but not for a long run. It should be based on the water parameters. Measure water parameters before or after each water change for a few weeks. If the results are worse than your desired levels, do more water change next time. If the results are better, do less water change. You will find a sweet spot sooner or later.

When you add more bioload or fish & coral growth or upgrade equipments like skimmer, you will have to adjust volume of water change accordingly.

 

[JohnK]

Just to add,

Thinking of water changes being largely for removing nitrate is kind of outdated. Most modern reef systems have adequate means to keep nitrate from accumulating in the first place.

What water changes are good for is replensishing trace elements and anything else we don't/can't monitor and supplement, as well as removing whatever other wastes or chemicals that might accumulate.

My advice would be to continue to change about the same % if the total system volume that you already do for water changes

 

[Yariel0527]

I don't know if I am doing this right but I have a 215g+ 62g sump fuge. One day I was doing a masive water change and this came on my mind why should I do a 10% or 20% water change a week why not do a small water change every day that will = the amount of water that I used to do a week and will be less tressfull and will benefice the system. That's what I though! so I decide to do a automatic water change set up that will change 5g tree times a day and since I have done that I have an dramatic change in my system corals are growing faster tank seems healthy and there's no mess with the nutrients at all.

 

[JayM]

if you can change 5g/day, and keep your parameters in line, that's a great way to manage waste on your system.

 

[Yariel0527]

i been doing it for a while and it works.....

 

[delta]

Personally I would skip the sponge of a DSB as eventually it will need to be removed along with all that biolaod it will absorb. To each their own.

Water changes are simple keep the same percentage

Reducing the water changed will reduce the amount of excess nutrient being removed from the system, more for the DSB to absorb.

 

[SteveDola]

is there a reason why you want to cut back on your WC %?

when doing a WC I never have a problem with doing 5, 10, 15, 20 ect...its just getting everything together to actually DO the WC. Man, I miss my fish room.

 

[honeypotGlen]

Some great points listed here. I really enjoy the conversation. It sounds like the best approach is to keep the % change for total system volume the same, and then adjust the change amount/frequency based on the parameters I am reading. Great point about increasing the stress on the dsb with fewer changes. I also like the idea of daily small volume changes instead of weekly. So if the nitrates are holding at zero, the change amount can be reduced slightly until nitrates start to go up. Then increase the amount changed slightly and stay at that level. If nitrates start to show again, then something has changed; the dsb or other filter needs to be changed, something died and is rotting, more life was added to the tank, or something else. Is that in the ballpark?

Happy Mother's Day to all you mommies out there.

 

[delta]

Problem with basing water changes off measured nitrates is, when you do something in a reeftank it takes time for the effects to show. So if you are not doing a enough it will take awhile to show. The DSB will buffer that even more. So if what you are doing is not working the DSB will hide it longer.

 

[honeypotGlen]

delta - OK, makes sense. But, what measurements are best for monitoring and tweaking water changes?