"Mean_Chlorine" wrote in message
...
Thusly "2pods" Spake Unto All:

This is very helpful to me as both my Juwel tanks ( 400ltr and 60ltr) ph
drops all the time.

That is possible, but unlikely. If you have, say, very large amounts
of driftwood or peat, or add CO2 to the tank, or you only use RO/DI
water, then you can get very low pH. Otherwise it is almost impossible
to get a pH unsuitable for fish in aquaria; pH is really a non-issue
in aquaria except for advanced aquarists, and then only because those
screw around with water parameters a lot (and usually unnecessarily).
Limestone is good because it smoothes out fluctuations and steadies
the pH at a nice level, but even without you are unlikely to see
dangerously low pH's unless, as I said, you're an advanced aquarist
Liqiud API test kit says 6.0, but I'm not so sure, as even after a 20%
water
change it only goes up to 6.4.

Have you tested your tap-water?

Yes, it's dead on 7.0

What does your waterworks say the pH of your tapwater should be?

7.0

So assuming I want to use crushed coral or limestone (any online UK
sources
? ), how much would I need for each tank ?

It's impossible to say, but the beauty of it is that you can't hurt
your fish by overdosing. Put some shells or something in, see if it
helps, if not, add more.
But I suspect your real problem is with your pH test kit - in most
cases when people measure really low or really high pH in their tanks,
it's really a case of inaccurate or aged test kits.

All three test kits, of different brands ?

The only difference between the affected tanks (400 and 60 ltr) and the
unaffected tank (240ltr) is the fact that the plants in the low pH tanks
(Cabomba, Watersprite, Hygrophillia) are growing well, while the "normal pH
tank (6.8 - 7.0) has less plants and has lots of algae.

All three tanks have gravel and use the same dechlor with a weekly water
change.

Also, the 400ltr has a Rena XP3 external with a bio compartment.
Would I be better putting the coral inside the filter ?

You'll get faster/bigger effect the more finely ground the limestone
is, and the more water flows past it, but the effect will never really
be either fast or big. Limestone simply reacts slowly at pH's around
neutral.
A quicker way is to directly modify the alkalinity of the water
through adding bikarbonate, but when it comes to pH quick changes are
not always a good idea, and I normally suggest using limestone
instead.

quick = bad for fish

Peter