Water changes ?

[Lesely]

HI, have a silly question to ask
I have a 260 gallon mixed reef tank. We live in Australia and during the summer months particularly lose a lot of water.
I have a 18 gallon ATO container that gets used over a 2-3 day period. I am very aware of the salinity drop with that much RODI water entering the tank over a week. So I alternate the fills on the ATO container between fresh RO and salt mixed water.
If I am using approx 112 gallons of saltwater (roughy) a fortnight and parameters are good do I still have to do the 200 litre water change I normally do every fortnight ?
It seems to me that most of my water is slowly being changed over that fortnight anyway ?

 

[kbuser92]

Yes you do. And the salinity will not drop with topping off if done properly. Only H2O evaporates, not sodium chloride, magnesium, calcium, strontium, iodine, etc...those minerals, both major, minor and trace are, however, being used up by your corals and inverts, and a small degree, by your fish. That is what you are replenishing through waterchanges. Of you have a small bioload and just a few corals, you probably don't need weekly changes, but bi-weekly or monthly, even, could suffice and maintain a happy, healthy tank. If you're like some of us and you have a demanding tank with lots of hard corals, then weekly would be a minimum and you would possibly still be supplementing calc, alk and mag.

 

[ErinCahir]

Big +1 to @kbuser92 . The only thing that evaporates is the water. Topping off with salt water is only going to raise your salinity.

 

[Lesely]

hi, thanks for replying.
I understand that salt doesn't evaporate. But I am wet skimming with large skimmer too and over a period of a week my salinity starts at 1.025 and within the 7 days it is down to 1.023-1.024 so I do actually top up with salt water 2 x a week and it keeps a very steady 1.025

Do you still say I need to continue my 200 litre water changes every fortnight ?? Or do you think I could go to monthly changes if all parameters are good ?
Do you have to do fortnightly water changes if all readings including the main cal,alk,mag are good ?
Thanks for your help !

 

[kbuser92]

Like I said above, I would still do them at least monthly at the very least.

 

[d2mini]

I don't know what a fortnight is. haha
But +1 to above... You should still do water changes. I've heard of people attempting water changes by wet skimming, but never really heard much about the results.

 

[kbuser92]

A fortnight is 14 days.

 

[Lesely]

I have never tried to water change by wet skimming, with 1000litre tank may take a very long time. usually blast off rocks, clean glass etc and then 200-250 liter change direct from display tank every fortnight. I am using NOPOX and it is recommended that you use a very wet skim, since doing that I have been going through twice as much water as I have been the last 8 months, so thats when I started to use some saltwater in the ATO container and found the trace elements were holding better as well as salinity. I will probably just keep an eye on things and change every month now instead.

 

[kbuser92]

Sounds like a good plan. I wouldn't do any more sparse than monthly, though.