As a complement - from my build threadI used to do religious water changes on my prior tanks, but I stopped doing them with my current rebuild, and I've been happy with it so far. Full disclosure: I am only now starting to add SPS to the tank, so only time will tell, but here's my thinking...
While water changes can clearly help, it’s also clear that they aren’t sufficient on their own, but it's possible that other methods can be sufficient without water changes, as long as you have a thorough plan.
There are 2 main reasons stated to do water changes: to get bad things out (pollutants, N and P) and to put good things in (trace elements). Let’s look at the math using the following assumptions:
- Water change (WC) is the only method of adding the good or removing the bad:
- System generates 10 pbb of PO4 each week
- System uses 10 pbb of trace element X each week
End of Week PO4 pbb Generated DT PO4 before WC Removed with WC Added with New Salt Water DT PO4 ppb Remaining 0 - 1 10.00 10.00 (1.00) - 9.00 2 10.00 19.00 (1.90) - 17.10 3 10.00 27.10 (2.71) - 24.39 4 10.00 34.39 (3.44) - 30.95 5 10.00 40.95 (4.10) - 36.86 6 10.00 46.86 (4.69) - 42.17 7 10.00 52.17 (5.22) - 46.95 8 10.00 56.95 (5.70) - 51.26 9 10.00 61.26 (6.13) - 55.13 10 10.00 65.13 (6.51) - 58.62 As you can see, water changes alone won’t cut it, so you must use other methods to remove the bad and add the good, even if you do water changes. Sure, a 10% water change is an immediate 10% improvement when other methods are more gradual, so you can see the immediate benefit. And I suspect there is often a correlation between religious water changes and good upkeep generally. If your other methods aren’t thorough, or if you get lazy when you stop water changes, then skipping water changes can be bad.
End of Week TraceX Pbb Used DT TraceX before WC Removed with WC Added with New Salt Water DT TraceX pbb Remaining 0 100.00 1 (10.00) 90.00 (9.00) 10.00 91.00 2 (10.00) 81.00 (8.10) 10.00 82.90 3 (10.00) 72.90 (7.29) 10.00 75.61 4 (10.00) 65.61 (6.56) 10.00 69.05 5 (10.00) 59.05 (5.90) 10.00 63.14 6 (10.00) 53.14 (5.31) 10.00 57.83 7 (10.00) 47.83 (4.78) 10.00 53.05 8 (10.00) 43.05 (4.30) 10.00 48.74 9 (10.00) 38.74 (3.87) 10.00 44.87 10 (10.00) 34.87 (3.49) 10.00 41.38
Here’s what I’ve used to get the bad stuff out in place of water changes:
Here’s what I’ve used to add the good stuff in place of water changes:
- Filter roller (or socks or pads) for larger organics and floating debris
- Skimmer for organics
- Algae Turf Scrubber for excess N & P
- ROX carbon for pollutants and any tint in the water
- Bare bottom with high flow for detritus on the bottom
- Blowing off rocks and bottom weekly to direct detritus to filter roller and skimmer
- Periodic treatment with a product like Waste Away to remove any build-up
- ICP to confirm no excess bad staff
- Water change only if directed to do so by ICP (hasn't happened, at least so far)
Water changes can also introduce opportunities for error (forgetting to plug something in, miscalculating the salt added, spills, etc.).
- Triton 4-part dosing (includes Alk, Ca, Mg and trace elements)
- Specific manual “fine tune” dosing of only those trace elements identified as deficient by a regular ICP test
Other reasons for doing a water change?
On balance, a solid no-water-change process seems better to me in theory, and it has held up in my first year of the rebuild without corals. We'll see if I need to modify or even abandon my approach as I move forward with SPS.
- Cost? – For larger tanks, the cost of salt for water changes can be more than the cost of an ICP test. It’s the opposite for smaller tanks. Even so, I would do ICP tests either way to be sure that I have sufficient good stuff and no excess bad stuff.
- Vacuuming sand bed? – I designed around this, but I suppose you could also vacuum directly to your filter roller/socks if you still wanted to avoid water changes. Never tried that.
- Restart? – I suppose there could be some other “restart” benefits…? Maybe the good bacteria gets a jump start when fresh water is added? I doubt it, but maybe?
As many understand - i do not do any WC. In a recent poll at R2R shows that is only around 9 % that only change water when it is needed. There is at least 4 different argues for WC in this thread.
1) The need of adding trace elements that normally will be depleted during a time lap.
2) exporting nutrients
3) exporting "bad compounds"
4) Cleaning of different compartments from detritus and organic matter
Let me first argue around standpoint 1.
Trace elements is for me rather essential because many of them have known and unknown biological importance. My goal as the first choice - try to have near NSW concentration of them and as a second choice - dose daily and in this way create a steady flux of just this element.
Before ICP testing - WC was the only way to guarantee that you did not build up dangerous amount of some trace elements because of dosing them. A blind dosing could be dangerous in the long run. Today - a periodical ICP test give you a snapshot of the concentrations before you build up dangerous concentrations. Even the concentrations of trace elements that in NSW is so low that ICP can´t show them - an ICP test shows if you are over the threshold or not.
With ICP testing - it is possible to dose trace elements (and macro elements too) in a safe way
Does WC with the finest quality of synthetic dry salt mixes guarantee NSW levels of trace elements (and some macros) or even if you have it in your actual WC mix or not?
I will say NO. Why - it is math and physics.
Math
When you mix your salt water - yo normally use between 36 - 40 grams dry salt mix to 1 l of water in order to reach 35 psu. In this exempel I use 40 g/l just for simplify.
NSW concentrations of - for exempel
Manganese -> 2 µg/l (ppB) = 0,002 mg/l (ppm)
Zink -> 4 µg/l (ppb) = 0,004 mg/l (ppm)
Iodine -> 60 µg/l (ppb) = 0,06 mg/l (PPM)
Strontium -> 8 mg/l (ppm)
This means that every 40 g salt mix should contain 0,002 mg Mn, 0,004 mg Zn, 0,06 mg I and 8 mg Sr.
Every kg of salt mix (good for 25 l) should contain 0,05mg Mn, 0,1 mg Zn, 1,5 mg I and 200 mg Sr
This is difficult to obtain but possible to do if you do the mix and use all of it in one batch. For me - I want to change 10 % (30 l) - I should do a mix of 1,2 kg salt that contain 0,06 mg Mn, 0,12 mg Zn, 1,8 mg I and 0,24 g Sr.
This doable if I mix and use all of it in one batch.
However - this is not the way it works. You buy - let us say a 22 kg bucket and use maybe 1,2 kg of this in each WC batch. This 22 kg batch should contain 1,1 mg Mn, 2,2 mg Zn, 33 mg I and 4,4 g Sr. And now - it needs to be evenly mixed because you take out only 1.2 kg of dry salt mix
Further on - before it reach your home - this 22 kg bucket have been done in a factory. if they mix batches of 22 kg - it is ok - but I doubt they do. Let us say that they mix 1 metric ton in every batch (it is a small factory)
Physical
This means that they have to in every 1000 kg dry salt mix put 0,05 g Mn; 0,1 g Zn, 1,8 g I and 200 g Sr. After this it needs to be evenly mixed. This is the elephant in the room - it is impossible to mix these small quantities in 1 metric ton of salt.
And - there is impurities in other salts that´s in use in the mix - the finally trace content is a lottery.
I hope that this math (if it is correct but even if it is 10 fold wrong - it still stands) will definitely kill the argue - I do WC in order to guarantee my levels of trace elements
Sincerely Lasse
Note
In my post above - I talk about synthetic salt mixes. There is other commercial salt mixes based on a solar evaporative processes and boosted with some compounds that disappear during the evaporative process. There could the content and spread of trace compounds and some macros really be the same as NSW. In the start of my aquarium (and if I need a WC today) - I use these types of salts. However - I have noted that sometimes especially heavy metals can be boosted of these salts - or at least the one I use.
Sincerely lasse
Sincerely Lasse