Stupid pH

[Jaded_Pulse]

A couple of weeks back, I realised there was shells & coral grit in my substrate which was making my pH really high (8ish). All fish doing ok but it really worried me. So changed all the substrate & with small waterchanges, it's back down to around 7.4. Thing is, out of the tap, it's smack on 7.0, & when I tested tap water with declorinator/dechlorimator (if that's a word) in it, it was slightly acidic, around 6.8.

So basically, when I do a water change, the new water is around 6.8. Within a day or 2, it's swung right up to about 7.4!! Everyone's still doing alright (4 colombian tetras, 4 black widows), but I'm worried coz I know that isn't good for them. All that's in there besides the new coral/shell free gravel is:

heater & powerhead filter (obviously not the problem)
1 small terracotta pot (told that was safe to put in)
5 plastic plants with plastic weights (nothing that bubbled when I vinegared them)
1 small cave (brought from my good lfs & washed well before adding)
1 aerator thing - it's a dragon that attaches to an air line that runs out of the tank to an aerator, & makes bubbles come up from the dragon (brought from dodgy lfs but I don't see how they could stuff this up - unless paint on it could be a problem?? But then again the cave's painted....)

So, any ideas?? Temp's pretty constant at around 27 degrees celcius. I really don't know what to do!! I don't really want to add pH down coz if it's something in the tank it'll only go back up again......any advice would be very much appreciated.

Thanx!! Michelle.

 

[konrad05]

NO2 and NH3 both increase pH when they dissociate in water, you might want to check for possible high levels.

 

[Jaded_Pulse]

Uhhhh.....wouldn't the NO3- act as an acid since it's nitrate salts are soluble so the ions would dissociate, & the dissociated NO3- is basically what makes nitric acid acidic?? NO2- also, by my reasoning would make for a more acidic solution (lower pH) rather than more alkaline.....I know I finished senior chemistry nearly 6 months ago but unless my stupid brain's completely abandoned me (quite possible), I don't see how this would be my problem........thanx heaps for the suggestion though

 

[kent]

i have no idea where u study chemistry but NO2- acts as a base in water.... therefore it's possible for high levels of nitrites to increase pH. and also, nitrates and nitrates are not the only free ions present in ur tank , so u cannot really say that all hydronium ions bind with NO2 to form nitrous acid or with NO3 to form nitric acid...Nitrous acid is a weak acid; thus, you cannot say that it will bring the pH down even if some NO2 ions bind with hydronium ions..

just contact me for any further questions.

 

[Jaded_Pulse]

lol yeah I know, I just tried to edit it coz I completely read Konrad's message wrong but it didn't work, need shooting I does. Anyhoo, ammonia's testing at 0, & I'm getting a nitrite testkit next week, but fairly sure I'm cycled anyways. Thanx for the help, sorry I'm stupid

 

[silver]

8.0 for a PH reading isn't THAT bad and shouldn't send you into a panic unless you have fish that absolutely need to be in lower PH!!!

I'd leave it all alone and not worry!!! If you baby fish toooooooo much it is worse then letting them adjust to certain things.......kind of like antibiotics and the problem us humans are having lately. They will be so darned accustomed to levels of everything being spot on and perfected that if something was to go wrong or fluctuate a bit it might have very adverse affects on such "babyed" fish.........

Just My .02

 

[Silly me]

first off, a PH swing of 6.8 to 7.4 in two days is not that bad.. I have found that our local tapwater is very soft and the PH drops from 7.8 to 6.8 in a single day if I just leave it standing in a bucket.

The big problem is if it keeps changing from 6.8- 7.4 to 8.2 to 9.3 - lots of dead fish

If the climb stop as 7.4 that fine. in my planted tank I have a I have a constant swing from 6.6 in the mornings and 6.8 in the afternoon..

Also you only adding 25% of the PH6.8 water to the tank the other 75% water is still PH7.4 so the PH might only drop from 7.4 to 7.2 in the water change??

 

[sinistral]

Nitrous acid may be a weak acid (conjugate base NO2, pKa=3.3), but Nitric acid is a strong acid (conjugate base NO3, pKa -1.3).

As long as denitrifying bacteria are converting Ammonia to Nitrites to Nitrates essentially as rapidly as they are being produced, over time the net result of this nitrogen cycle is a drop in pH (becoming more acidic).

Anyways, I second what silver and Silly_me indicated. I'd recommend testing the tank right after you do a water change to see what the pH actually is after a change; you may not be introducing as dramatic a pH swing as you've indicated.

Are the elements in the substrate that contributed to the pH of 8 still in the tank?

 

[Rudy2860]

aged water keeps a stable pH, try agitating the surface of the water with say an air stone or two that will stablilize pH

 

[Bangin]

Are the elements in the substrate that contributed to the pH of 8 still in the tank?

I imagine they're tiny bits of coral and shell which will continue to affect the PH.

Crushed coral is used to increase the KH, which in turn increases the PH.

I wouldn't want that much of it in my substrate.