ph swings in pond. long post sorry, got carried away.

I have a small pond (100gallons its actually a large bath) with a lot of
plants and a couple of goldfish which have outgrown their tanks.

I added a filter, declorinated water, cycled the pond, put 2 fish in and
everything was fine, ph, nitrate and ammonia was perfect for a few weeks
with a bit of green algae on the sides.

Then i added the plants (oxygen weed) and the PH was swinging from 6.5 to 9
or even 10 in a daily cycle, a couple of weeks later I picked up some
ammonia on the tetra test kit (just about 0.3) and noticed a couple of the
fish were losing scales and not looking healthy. So they were bought back in
to their tank where they seem to be recovering well.

The pond has now been drained, painted with black bitumen, rinsed through 4
times, filters cleaned etc and is cycling as i type. but i need the plants
there to give the fish somewhere to hide as there are herons locally.

Now as i understand it, the PH swings are due to my water being too soft,
for a breakdown, see below
Hardness level SOFT No Standard Applies
Hardness Clarkes 3.6 No Standard Applies degree
Hardness 19 No Standard Applies mgCa/l
Aluminium 10 200 µgAl/l
Calcium 18 250 mgCa/l
Chloride 10 400 mgCl/l
Chlorine 0.16 mg/l
Coliform bacteria 0 0 no./100ml
Colour 1.55 20 mg/l Pt/Co
Conductivity 112 1500 µS/cm at 20
E.coli bacteria 0 0 no./100ml
Fluoride 922 1500 µgF/l
Iron 21 200 µgFe/l
Magnesium 2 50 mgMg/l
Manganese 3 50 µgMn/l
Nitrate 2 50 mgNO3/l
Odour 0 3 dilution No
Pesticides 0.0065 0.5 µg/l
pH 8.7 5.5 -9.5
Sodium 5 150 mgNa/l
Taste 0 3 dilution no.
Temperature 12.4 25 deg. celsius

Plumbing Metals

Zinc 8 5000 ugZn/l
Copper 14 3000 ugCu/l
Lead 7 50 ugPb/l



The PH of my water is actually 7.5 not 8.7 as above.

I`ve tried to get into understanding the various types of hardness and am
stumped as everything that changes the hardness also seems to change the PH,
I`ve been told to add bicarbonate of soda, but wouldn`t this push the PH up?
LFS suggested calcium carbonate, wich was quite intimidating until i
realised he meant chalk. What can i add that will stop the PH swings without
affecting the PH of my tapwater too much?

Also will marginal plants affect the ph like submersed plants? (i suspect
not as the leaves are out of the water, but I don`t want to go and buy them
and find out i`m wrong

One last thing, how long will a bucket of water take to dechlor with a 4"
airstone in it? I`ve been leaving it for 24 hours and changing a bucket a
day in the pond and 2 buckets a week in my tanks. Would it be safe to do 12
or even 6 hours per bucket? I don`t use dechlor as i don`t like using
chemicals unless i truly have to.

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