Tap water is convenient and inexpensive but you probably don’t want the chlorine added to an aquarium and if you’re adding a lot of new water such as the 50% water change in an estimative index fertiliser scheme this becomes particularly important. Accordingly it is pretty standard to use a water conditioner to neutralise nasties in tapwater that might be present. I use Tetra’s AquaSafe and have never had any problems. A full capful (note: the outward-facing top part of the cap is the dosing measure, not the inwards-facing larger part of the cap) is 10 ml which will work for 20 litres of water.
Note the ‘in tapwater’ piece: the product doesn’t magically fix aquarium water that has already wonked-out chemistry. If aquarium water chemistry is a problem, you need to fix the underlying cause rather than attempting to treat the issue, which water conditioner won’t be able to do successfully anyway.
Having done a 50% water change with the water conditioner if I need to add a little extra water, maybe up to 200 ml, to top things up afterwards I don’t bother adding water conditioner to that extra water on the thinking that there’s already lots of water conditioner in the tank now and with good mixing there won’t be any meaningful extra stress that would merit faffing around with adding water conditioning agent to small water volumes.
Water analysis of AquaSafe
I recently sent a number of different water preparations to Oceamo for analysis. Several of these were prepared with “following the instructions” addition of AquaSafe. I also looked at the effects of AquaSafe plus CupriSorb (a copper removing resin) vs. just CupriSorb itself without any AquaSafe. The results give insights into what AquaSafe is and does.
| Water Change Preparation | Mg mg/L | I µg/L | Cu µg/L | Zn µg/L | Pb µg/L |
|---|---|---|---|---|---|
| Prep #1 with AquaSafe | 5.00 | 10.96 | 4.92 | 11.77 | 0.057 |
| Prep #2 with AquaSafe | 4.70 | 11.87 | 4.01 | 8.17 | 0.089 |
| AquaSafe + CupriSorb | 4.98 | 10.96 | 5.91 | 15.63 | 0.14 |
| CupriSorb only | 4.85 | 2.26 | 0.78 | 0.98 | n.n. |
AquaSafe adds significant iodine, but not magnesium
Promotes vitality, as well as growth and well-being, with added iodine and magnesium.
Adding AquaSafe to water change water looks like adds (give or take) 8 or 9 µg/L iodine. I don’t know whether that’s a biologically meaningful level sufficient to promote vitality, growth or well-being, but it is at least measurable. On the other hand, if AquaSafe is adding magnesium, it isn’t to a level that materially shifts my incoming Mg concentration of almost 5 mg/L (CupriSorb only row).
AquaSafe stops CupriSorb from working
For shrimp keeper this is a big one. I have been using Tetra AquaSafe for years in the Shrimphaus. AquaSafe says that it:
Immediately neutralises dangerous chlorine, chloramine, copper, zinc, and lead found in tap water.
Chlorine and chloramine sure, likely by reduction chemistry with something like sodium thiosulfate which is fast and converts both over to relative harmless chloride (like the back half of a tiny addition of table salt).
Copper, zinc and lead though need different chemistry. Here AquaSafe is going to try to lock these away by chelating them with EDTA much like how iron is stablised with EDTA chelation. ‘Neutralise’ is not the same thing as ‘remove’. CupriSorb actually does removal. Free metal ions like Cu+2, Zn+2 and Pb+2 get locked onto the CupriSorb resin and removed because I discard the resin after the water change water has thoroughly flowed over it. You can see from the CupriSorb only row that works a treat, with dramatic reductions in all three metals, but if AquaSafe is around, the CupriSorb doesn’t work anymore!
The likely mechanism here is that CupriSorb is looking to bind free metal ions, but if those ions are already bound up by EDTA, they aren’t free anymore so CupriSorb doesn’t grab them. This is a problem, because unlike the CupriSorb that never gets into the Shrimphaus, the AquaSafe EDTA-chelated metals DO get into the Shrimphaus, in the water change water.
AquaSafe bound copper is not fully shrimp safe
My caridina shrimp only started breeding successfully when I removed copper first with CupriSorb and then added water conditioner after the copper had been removed. Turns out 5 µg/L copper is a deal-breaker for caridina breeding, even if that copper is bound up with EDTA from the AquaSafe. Likely this is because the EDTA isn’t 100% stable and so breaks down over time either in the water column or at the shrimp gill membrane and releases enough free copper to be a problem.