Okay, I have strangeness....... I have done a couple of days of water changes, (in the overdosed empty tank as well - so both will be at the same pH).

I come to check the water I had for last night and it was at 7.0+ without adding anything to it! (left standing for 24hours, btw). I got rid of that and got fresh water and again it tested 7.0+. Can tap water change its pH like that? (it was testing out of the tap at ~6.4). If this is the case then it could be the reason for the problems I have had. :/

Could be a few issues Sem.

The regular water chnages have increased the level of KH (common) which then in turn pushes up pH.

Tap water is being read immediately as opposed to letting it stand for 24 hours (recommended).

Local water company has flushed the pipes recently.

Local water company is using water from another source.

That was the type of thing I thought it may be, but I was just checking incase I was missing something......... this would be a lot easier to manage if the tap water stayed constant....and if this big of a fluctuation has happened in the past it is the number one suspect in the previous tank disaster!

The one thing this is doing is making me check water quality at more regular intervals, so I will be more likely to see a problem while I can still do something about it......and if the tap water is generally 7.0+ then I will just have to buffer the fresh water up to that pH, if/when the level drops again. (much less messing with the water than I thought I was going to have to do).

I have a grasp on things now, though I'm sure there will be something else. I'll be back.

Bear in mind that the nitrogen cycle is an acidic process. Those in uber hard water areas will never see this occuring in tanks of course, but generally speaking for others, a slight shifting from neutral to more acidic levels can occur over time.

They key to monitoring is just what you said Test the old water weekly for the usual 4 culprits, pH, ammonia, nitrite and nitrate just before you start the water change. That will then give you an idea as to any action you need to take. Tip: Keep some bicarb of soda in the cupboard for any emergencies.

Someone once here said that they keep water, not fish. The fish look after themselves. I like that!

Its happening again!

I have been taking proper care of both tanks, doing regular water changes, checking for ammonia. etc, but I have let the pH measurement slide as I have been setting up a new tank, (there is a post in the tropical section regarding that).

I have lost my female guppy on Sunday morning, , i changed the filter, (as it was due), and did a small water change. I noticed tonight that my male was kinda sluggish so I ran for the test kit and found this.

Ammonia: 0 - NitrIte: 0 - NitrAte: 5, but pH 5.1!!! I checked my small empty tank and it is similar 0/0/0/5.3

I took out the filter and added a little Crushed Coral, and am doing a small water change.......the tap water tested at 7.83 directly out of the tap, (although it is generally ~7 after a day), and that reading was taken rather quickly. I am left with a rather unhappy looking male and some fry swimming around the tank, while a small group of fry are at the edge of the tank in obvious stress.

I panicked a little and am worried that I may be upping the pH level too quickly? As the Ammonia levels are not rising yet, I am guessing that it has not had an effect on the bacteria?

I have taken the CC out of my NEW tank and done a couple of water changes, of around 50L total, and the pH still sits at ~8.8! Yet the pH in these two tanks has just crashed......

Is there anything else I can do?

Do you know what the kH of your tap water is - can't remember if you have it or not? Low kH is the issue. The biological activity responsible for processing ammonia uses up carbonates so if you have a low kH, it can all be used up between water changes. kH is what stabilises pH; when kH drops, pH follow it. You can use crushe coral or oyster shells in the filter to maintain kH between water changes, but you will also need to match the new water to the tank pH an kH by ading bicarbonate of soda or a proprietary buffer like Seachem's Alkaline Buffer.

The reason for the high pH in the other tank is, I believe, due to calcium and/or salt deposits from its previous life as a marine tank. Unfortunately the only thing you can do there is take it all apart, clean all the calcium deposits away and then start again

I have taken kH and gH readings and they were both very low, I can't remember the exact levels, but you told me CC was the answer. Unfortunately the possible calcium contamination has confused matters and I was a little worried about using it, (after seeing the high pH in my Juwel tank).

I'll keep these two threads separate, as it will only lead to confusion otherwise....so after I changed some water in the Biube, the pH has changed from 5.1 to ~5.4, a sharp jump, but still not anywhere near safe. How fast can I go about this without doing harm to my remaining fish? I just changed 5 litres, (12.5%), of the water in the tank.

I thought I had this under control doing regular water changes......if I save these fish would bi-weekly water changes help?

Could I dose the tank with a tiny bit of bicarb to up the pH to safer levels or is the sudden increase going to do more harm than good?

Twicce weekly changes may be enough - it depends how quickly the kH in the water is used up. It's one of the reasons Discus youngsters have huge daily water changes. Because particularly with wild caught Discus and their immediate offspring, a very low pH is needed, the water will also be low in carbonate buffers. Very acidic water is harder to keep stable and lower kH means less biological filter activity so the water nees frequent replenishment to keep pH stable.

It would be safest to use a buffer (coral/oyster shells) in the tank/filter for stability and match water changes by raising kH/pH with bicarb. To raise the level from where the tank is now more rapidly you can do daily small water changes with bicarb in the fresh water so long as the pH in the tank doesn't rise by more than 0.2 each time. Doing it that way can be tricky though due to the tiny amount of bicarb need in the water for a 10% change on a smaller tank and you will need to test kH and pH levels in the tank, tap water, and as you add bicarb so that you don't push it too high, too fast. Add the bicarb a tiny bit at a time and wait a few minutes after each addition before testing.

I tested the water, it dropped again......4.8.

The fish are actually swimming about and seem a lot less stressed but I cant imagine this is going to last for long with the water pH crashing like it is. Its not a good feeling, knowing I have to gradually adjust the water, when the situation is so serious.

I have taken 5L out again and am dripping fresh water back into the tank, (trying not to make sudden changes). If I am adding the higher pH water like this will I be able to do it over and over until the pH gets to a safe level, should I still be looking at a .2 difference per day? (I should only be able to do 3x5L at most, in a day, dripping the water in.)

It doesn't look like last nights water change had any long term effect, as it seemed to drop a further 6.0, (or 3.0 from the original measurement). I am adding carbonates back into the water with the water change, though this doesn't seem to be making a difference? Is there anything else I should be doing, (adding the tiniest amount of bicarb for instance), to help or will the water changes eventually start showing results?

Are you sure your pH test is accurate? The drop seems very drastic even with a low kH. What size is the tank and what stock do you have in there? For pH to fall so rapidly there must either be a lot of biological activity or there is something else in the tank acidifying the water. Do you have any bogwood, leaves, peat etc., in the tank?

You can do two or three small changes a day spaced a good few hours apart to raise the pH by .2 on each change, but you do need look at potential aggravating factors and add
a more permanent buffer into the tank or filter to maintain it, otherwise you will always have these fluctuations between water changes.