Ph Tds Gh And So On

[andyG44]

My tap water is usually hard with TDS of around 240 and pH 7.8-8.4.
 
Many fish and other things are best at 6.5-7.5 range with 7.5 given as best overall.
 
I can mix RO water to lower the pH, easy, and that will also lower the TDS down to 100 maybe to achieve the pH=7.5.
 
Do I need to care about the GH or KH since I have no kit to test it?

 

[techen]

I will give you a simple answer, Don't try to change your PH at all. Everytime you water change and such you'll change the PH over and over and over again, It's just not good for fish.
 
If the LFS you go too is local, It's most likely using the same water supply as you and therefore the same PH etc, So..... There is no issues, They've adjusted to that PH level and should be 100% prefect in your tank, Dont worry about it.

 

[Byron]

I would like to expand this thinking.  AndyG44, yes, every aquarist should know the GH and KH of their source water; and the pH which is inter-related.  I am not saying everyone should fiddle with these for this or that fish...just that every responsible aquarist should know what comes out of the tap.  Then select fish that will manage.  You can ascertain the GH/KH from your municipal water authority.  I wouldn't waste money on test kits unless of course you do go down the road of adjusting parameters.
 
Some aquarists will adjust water chemistry, and sometimes this is absolutely needed, depending upon the source water and the fish species, and your intentions.  One of our members who has gone through this is TwoTankAmin, and in one or more threads he has detailed how he achieved it for a tank of wild Altum angels, and of the absolute necessity of doing so in that situation.  Some soft water fish will not adapt to hard water (relatively speaking) especially if wild caught, while some will manage with harder water but not spawn, and some others will manage and even spawn.  The "manage" is usually relevant to the lifespan, and important factors are the fish species, age, and the degree of parameter variance.  The effects of harder water on soft water fish, or the reverse, sometimes take months and even years to be noticed, when the fish just suddenly dies "for no reason."  Again, this varies according to species.
 
The fish in the local store usually do not stay there long (or so the store hopes/intends), so they in fact have not had time to actually adjust to the local water; this can take generations for many species.  The more common "bread and butter" fish have been commercially raised for decades and this makes a difference.  For some species, the parameters at the source of the fish (which could be private breeder, commercial hatchery, or nature depending upon the species and origin) is what we really need to know if we are considering fish with preferences significantly different.  This is not always easy to ascertain.
 
Byron.

 

[TwoTankAmin]

One of the easier to understand basic explanations of water parameters and changing them can be found here:
http/fins.actwin.com/mirror/begin-chem.html
I suggest you have a read.