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Rainwater from a butt - de-oxygenated?

Joined
3 Jan 2016
Messages
383
Location
Woking, UK
When doing my 50% water change, I use 9 litres of rainwater from my water butt, mixed with 3 litres of unsoftened tap water. This gives me roughly the 3° KH and 6° GH that I'm after, and I can tweak the GH up a bit by adding MgSO₄ solution if necessary. I use Seachem Prime as my dechlorinator, and use a full-tank dose (only 0.5ml for my ~20 litre tank, so it would be impossible to measure any less). I boil a litre or so of the rainwater to bring the new water up to temperature.

I often notice that the gill rate of my Otocinclus has risen dramatically after a water change, and this seemed particularly bad yesterday. They were also very restless, and the chili rasboras were nervous as well - schooling very tightly and patrolling the tank rapidly. Most of the blue cherry shrimps seemed fine, but I did see one swimming very erratically and seeming to have difficulty staying upright. There also seemed to be a migration of snails heading up the glass towards the surface, within half an hour of the water change.

I decided that there might be a problem with lack of oxygen in the new water, although I must admit that none of the fish were gasping at the surface. To combat this, I added 15ml of 3% Hydrogen peroxide in the hope that it would provide some emergency oxygenation. (Actually it may have been after this that I saw the shrimp swimming erratically, not sure). After this, the chilies seemed to calm down slightly over the course of the next hour or so, and perhaps the Otos' gill rate slowed very slightly although still too fast.

So, does anyone know the typical oxygen content of rainwater that has been sitting in a water butt for a few weeks? I can't decide whether it's likely to be de-oxygenated or not. I am drawing water from the bottom of the butt.

Is there any point trying an oxygen test kit?

I can't think of any other contamination: the water butt is plastic, as is the house guttering. The roof tiles are old, so shouldn't be leaching anything into the water any more. The bucket and jug that I use are not used for anything else. That said, I don't know if it's my imagination but the tank didn't look quite as sparkly clear just after the water change - but that could be normal.

The tank looks okay this morning although I haven't yet done a head count.

Any thoughts? Would low O₂ level cause rapid gill movement in one species, but 'stressed' behaviour in another species, without any gasping at the surface?
 
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Just a thought...

The Epsom salt I'm using is a normal gardening product. I keep a stock solution with 44g dissolved into a litre, and dose 1ml of this stock solution per litre of tank water to raise GH by 1°. Yesterday I dosed 10ml into the new water to give a small increase (otherwise I find the GH reduces over time, perhaps as plants are using the dissolved salts), and tested the tank water after the change: 3° KH and 6° GH, which is exactly what I aim for.

Any problem with this? Could there be something else in the product that I don't know about? Maybe I'll try an ammonia test on my stock solution to be sure.

The data sheet for the product says it's only MgSO₄ heptahydrate, so shouldn't be an issue.
 
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Years ago, my brother did a 100% water change using water that had been kept very long in a water butt. All fish died. Yeah I also think it was from lacking of oxygen. And Prime just worsens the problem as it also reduces oxygen level.
 
Test the water in the water butt for ammonia and nitrite. Containers with stale water do go through nitrogen cycle.
Also, it's not a good idea to rely on matching the individual parameters when mixing water. Get a cheapTDS meter and mix the water to match a chosen reading, regardless of the individual readings of GH or KH. It's less risky on the fish that way.
 
I do have a TDS meter, and use that to verify that the new water is about the same as the tank. It's within 10-20, with the tank measuring about 130.

The rainwater tests negative for NH₃/NH₄⁺, NO₂⁻ and NO₃⁻.

For my next water change I'll try mixing the water the day before and leave an air pump running overnight.
 
Good ideation try and oxeye mate the water first. Make sure add prime etc at the same rate.
 
I wouldn't think the rainwater's oxygen content is the problem because in order for it to cause stress it means the remaining 50% of water in your tank is severely low on oxygen and it's easily tipped by the new water. An airstone or heavy surface agitation should fix that within 30min or so if that's the case. No need for hydrogen peroxide...

What is the KH, TDS of the tank water at the end of the week, just before you pour the new one? My guess is you are swinging the stats or there's something "fishy" in the rain water. It's pretty uncommon for TDS to remain the same after a week of no water change so to what TDS are you matching the new one? The Kh gets lower over time too but if you are doing 50% water change weekly it should remain solid stable at 3° KH. It's a small tank so it's easy get it wrong if you are adding rainwater.

Ottos can breathe from the surface and if oxygen is the issue, they'll be the least stressed ones in the tank, plus they'll shoot to the surface to gulp air. So the issue might be osmosis if you are certain nitrite and ammonia is not the cause.

There also seemed to be a migration of snails heading up the glass towards the surface, within half an hour of the water change.

They do that for various reasons and especially when the water conditions are not right, e.g low nitrite/ammonia lingering. Do you have algae issues? Diatoms?
I boil a litre or so of the rainwater to bring the new water up to temperature.

When you boil the water, you kill the hardness in it. It's a small tank so a little bit may go a long way.
When I've used MgSO4 it swings my TDS pretty heavily.
 
There's no measurable hardness in the rainwater - which is why I boil some of that rather than the tap water. As you say, boiling the tap water would destroy some of the hardness that I want. Any hardness in the rainwater is completely negligible compared to that in my Woking water.

I normally only test after the water change, otherwise it would get expensive. But next time I'll test before and after.
 
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You don't need to test before and after each time, just for now as means to figure out what's happening. If you haven't tested your tank water recently then chances are it's very different to the water you are adding. It may not be but I'd go the extra mile and investigate if they were my fish and make sure I am not shocking the fish each time.
 
Hi all,
I wouldn't think the rainwater's oxygen content is the problem because in order for it to cause stress it means the remaining 50% of water in your tank is severely low on oxygen and it's easily tipped by the new water. An airstone or heavy surface agitation should fix that within 30min or so if that's the case.
Because the water from the butt is cold, it should hold more oxygen, but if it was de-oxygenated it would form a layer at the bottom of the tank. I use rain-water, but I draw it off the night before I use it. You can't test for dissolved oxygen (with-out a seriously expensive DO meter), but you can test the conductivity with a TDS meter, it should be below 100 microS.
there's something "fishy" in the rain water.
Distinct possibility at this time of year because farmers are spraying Wheat etc with insecticides.

Can you add some Daphnia to the water butt? I work on a simple rule, if the water has swimming Daphnia it is OK to use. They use Daphnia a lot for <"water bioassays">, because they are sensitive to a whole range of biological pollutants. <"Evaluation of Daphnia magna as an indicator of Toxicity and Treatment efficacy.......">.

cheers Darrel
 
Adding some daphnia to the water butt is a good idea, might do that.

From what I've read, Prime only causes oxygen depletion when grossly overdosed. I'm adding 0.5ml to a 20 litre tank. Don't think that's going to be causing any problems.

I have ordered an oxygen test kit which should arrive tomorrow so hopefully I'll be able to confirm or eliminate that possibility soon.

I personally think it's unlikely that I'm shocking the tank with wildly differing water parameters. I do a 50% change with the same 'recipe' of water every week, which means that the parameters of the tank water are strongly influenced by the parameters of the weekly water change. Any alteration of the tank parameters in the meantime would have to be rather rapid in order to take the tank water significantly away from the parameters of the water change. There's probably a small downward drift in KH and GH (plants use the calcium and magnesium, and I believe nitrifying bacteria use carbonates), and a small upward drift in TDS due to accumulation of excess plant nutrients (although offset by the reduction in hardness) - and the pH of the tank water will be slightly lower than the new water due to CO₂ etc.

If I were to match my water change parameters precisely to the water in the tank each time, that would allow the tank water to continue its downward KH/GH drift, resulting in dangerously low buffering capacity. I think it's important that the new water continually 'resets' the tank water and pulls it back to desirable parameters, and provided the difference isn't too great that shouldn't be causing shock - especially since I'm not keeping hyper-sensitive species. I have kept freshwater tropicals for many years in the past, and have never before worried about precise matching of water change parameters - the only thing I'm doing differently this time is using rainwater from a butt.

My next water change will be Friday, give or take a day. I will do before and after water tests on the tank, including TDS measurements. My prediction is that there won't be a big enough difference to account for any fish stress.
 
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Quite a lot of fish breeders use rainwater to create conditions for the fishes Neon Tetras as a example you could just be unlucky were your location is as been mentioned by Darrel
 
Well, my oxygen test kit arrived today, which is extraordinary since I only ordered it yesterday afternoon!

I have tested both the tank water and the rainwater from the butt, and I do think oxygenation could be a problem.

The tank water measured somewhere between 5 to 8 mg/l, which according to the leaflet is okay but not particularly high for water at 25°C. The lights have been on for only an hour, so the plants haven't had much chance to re-oxygenate the water yet. The HC and Glossostigma are not yet pearling. I will re-test later this evening when the lights have been on for longer.

The rainwater from the butt measured only 2 mg/l, which is the lowest level that the kit can indicate. For water at outside temperature (probably about 10°C), that is very low. Given that this is the lowest level the kit can indicate, it's possible that the rainwater is even lower in oxygen than this.

So, I think that a 50% water change using water that consists of 75% of the rainwater that is very low on oxygen, when the tank's water is "okay but not high" means that there might well be an oxygen problem.

Next water change, I will definitely prepare the water the day before, and aerate it overnight - then I'll measure the O₂ content.
 
I know it seems obvious now but back in the day I seem to remember the so called experts recommending aerating the water butt constantly to stop the water stagnating...maybe there was something in it.
 
I forgot to answer sciencefiction's query about algae...

At the moment I have fairly low algae. I have a few small tufts of what looks like black brush algae (BBA), but it sometimes develops the 'antlers' characteristic of staghorn so I'm not exactly sure which type it is. Does staghorn algae have a juvenile form that looks a bit like BBA? Or is it even possible that there's some kind of symbiosis going on between those two types of algae? Anyway, this is a very minor problem; it is not spreading or growing at all rapidly.

Until a couple of weeks ago I had an outbreak of long green threads, and also much shorter velvety green algae in patches on the wood and Anubias leaves, plus a few green spots on the front glass. At that time I had a two hour period of light in the morning at 25% brightness - the purpose being to wake the fish so that I can feed them each morning. I decided that this might be the cause of my green algae issues so I reduced the brightness right down to 5%, which is still enough to wake the fish. Since then, the green threads and spots have vanished and the green velvet is slowly declining.

So as it stands now, I have only a few small tufts of BBA or staghorn and small, dwindling patches of green velvet that's starting to look a bit threadbare where the shrimps have nibbled it. The algae seems to be struggling to cling onto its existence, which is good!

I definitely don't have any diatoms - I did have brown filamentous diatom while the tank was maturing, but that suddenly packed its bags - possibly coincident with my starting to dose the TNC Complete at 2-3 times the regular dose.
 
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