Sera ph-minus - dummy question

[GuppyFish]

Sera's "pH-minus" label says to add 5 ml per each 20 litres of water.
So, should i add a full 100 ml bottle into my 450 litres tank at once ?
(currently in tank pH 8.3, kH 14)

I'm afraid that my red mirophyllum, alternatheras and nesaea feel no good due to such water hardness and would like to cut in most quick way.
I believe Sera gives correct instrutction on a label, but do they mean that ph lowering shall be done in a tank with no fishes and plants ?

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size: 171 x 62 x 45 sm. height is 45, so 450 litres
light: 4x58=232 Watt (2x Osram/77, 1 Osram/25, 1 Osram/10 +1 empty)
CO2: 5L barm+sugar+gelatin

[PeterGwee]

Folks measure pH/KH for a planted tank just for CO2 measurement and not much more. Plants do not care for a certain pH unless you go to the extremes...want CO2 just add CO2. Do not add anything to lower the pH..you will not help the plants at all.

Regards
Peter Gwee

[David]

You can lower your PH with fish in the tank provided if you are able to control that the swing is within 1PH point......anymore than that, its going to send the stress level of your fishes up the roof.

You KH of 14 is not really that bad as you can still go for PH of 6.9 or 7.0.....As what Peter has mentioned, use CO2 to lower your PH.....for you to have a KH of 14, do you have coral chips somewhere or limestone?....If that is the KH from your tap, then keep your fish population low so that you do not need to keep changing large amounts of water every week....and let the plants do its job to reduce the KH.

[GuppyFish]

no, i do not have any corals of course
yes, thus the gravil in my tank is a natural one from the river (sifted rvier gravel of 3-4 mm) it still have some more calcium than tropical one.

but the main problem is our water supply is pH about 8.5 and kH up to 20 !!!

i used a continuous water-flow of about 50 litres daily (btw continuos maintaining of above ph & kH + continuous new water + some CO2 kills "black beard" very well in my tank)
but since i see some plants feel bad (red myrophyllum) i stopped continuos changing in try to reduce ph & kh.

due to tank dimentions ( being optimal for the planted tank i beleive) and lamps clouse to water, the vaporization of water is rather fast, so anyway,
that means (or not ?) - i can not be sure that pH will go down upon some time "automatically" just by work of plants and fishes. but i hope it will