Fat Fish

I'm not 100% sure but I think you progress from newbie to jr member at 50 posts - that's round about where I noticed I'd moved up a grade 

Have you had a look in the attic? Because of tales of houses where the only mains water is the kitchen tap, whenever we've moved house I've sat next to the attic tank and got someone to run the bathroom cold tap to see if the water there came from the tank or the mains (water soon starts to run into the tank if the tap runs from the tank). All this because it is not safe to even clean your teeth in the bathroom if the cold water comes from the tank. Doing that would tell you which of your taps run off the mains and which don't.

You could always try sticking your head and shoulders into the hole and listening for water running in the attic 

Interesting reading SteveS, thanks for that.

Iron. Wow. I had problems with iron last year (detected by running polyfilter which turned bright orange). Natalia concluded it was leaching from the plant substrate under the gravel. I stripped both tanks down and removed the plant substrate - all was well after that. Im now thinking I should run polyfilter for a while again.

I phoned the water Company yesterday and was told to run the kitchen cold tap for one hour, checking every ten minutes. Philosophy being that this would flush the problem out. I was skeptical, but did as advised. After half-an-hour I was beginning to think what a waste of time/water. Then amazingly, at 40 minutes, the water was running clear again. I still left it the whole hour and the water was still clear. I live in hope that when I draw my 4 buckets tomorrow, the water will still be clear. I dont want to try it out before then because we are on a metre! (they credited an hour to our account for the "flushing"). And besides, I want to see that the problem wont re-occur in the meantime.

The good news for now is that I havent lost any fish since water change at the weekend. In fact, Ive gained fish - one of my oldest female mollies gave birth Monday night! She didnt wait for lights-out this time so I actually saw a wee fry pop out  (though I turned the lights off for her after that because she was trying to see off the other fish whilst giving birth!)

In an older house, a damp patch could also be a leaking tank! My elder son and his wife bought a 1940s house last year. The mortgage surveyor said he thought the roof was leaking but it turned out to be the attic tank on the point of disintegration. And back in the 1970s my father was getting a suitcase out of the attic and noticed a patch of rust on his tank. The plumber who replaced it said it could have developed into a hole at any time so it was a good job he'd found it.
More modern houses have plastic tanks so at least they shouldn't rust.

Curiouser and Curiouser!!!! You guys are really making me wonder what is in our loft! When we moved in, half the bathroom ceiling was peeling from damp (well, saturation actually!). Damp patches extended into the kitchen and hallway ceilings / upper parts of the walls, though not to the extent of peeling paint. The repair guys came and found a tile missing off the roof. They replaced it, peeked in the loft (head through the hatch!) and declared the missing tile was the cause. We took their word for it that nothing else untoward was going on........ I do hope they were right - I dont fancy sticking my head in that wee hole! To be fair, the ceiling does seem to have since dried out and the repair guys have painted the affected ceilings/walls with special paint. One or two small patches in the bathroom have started showing through again, but I gather damp is a nightmare to cover up without it coming back through.

We assume there is a tank of some nature in the loft. The property is around 50+ years old and we know that a new central heating system was installed just prior to us moving in. We guess thats when the open fireplace was blocked off.

Don, we too have softer-than-a-babies-bottom water in the sunny South West! I also thought that the higher pH would be better for my mollies so I tried to "acclimatise" the tank to the tap pH. For a couple of weeks, when doing a water change, I slowly added one bucket straight from the tap (correct temperature & dechlorinated of course!). A couple of hours later, I slowly added another bucket. Another couple of hours, I slowly added the third bucket and finally the fourth bucket another couple of hours later. Blow me, the tank still came out at pH 7.4  I concluded that trying to mess with the pH like that was worse than keeping it at the 7.4 its been stable at for the last 2^1/2 years. Thats when I decided to let the water stand, allowing it to drop to 7.4 before using it in the tank.
Really, it was only the black molly (Dreckly) that would strongly object to the water. The slightest thing out of the ordinary for her and she would break out in mould (saprolegnia). She was one of the two that died last Monday 

SteveS, your post about unpressurised central heating lost me. Sorry   

Hmmm could possibly be leaking, the house is about 110 years old so proably a rotten water tank. Needs to come out anyway as i said its been bypased by the combi boiler presuried system. Its ideal for me with my south americans think both my tanks are ph 6.2 harness 3-5 degrees.

Mollys can be funny things ive known people to keep them at ph 8 an brackish and they love it apparently. Im guessing your other fish are doing fine?  Sounds like trial and error but if the added tap water wether left to stand or aclimatised isnt affecting the tank ph then you may be okay. Am i correct in thinking you say the water is soft but the ph is 8 or so?

Do you mean leaving the water stand before using it in the tank, or the bit where I tried to "acclimatise" the tank to the tap?

I'm referring to the latter;  It won't affect the pH in your tank except, perhaps, for a very short time.

surely its better to let the tap water stand in order for the pH to drop equal to the tank before putting it in?

Hmmm... As a general case, I'm not convinced;  I don't see how it can do any harm though.

But I'm confused (again!

Don't be confused, if it works for you, go for it.