i have a 75 gallon tank with fish and bulb plant from the pet store. i have had them for about 9 months and doing great. now i am up grading to live plants with co2. we just started running off a new well for water my dh and kh are off the charts we have very hard water with that it means high ph. straight from the tap i read 8.1 for ph.plants are on order and will be here thur. or fri. if i run my co2 and drop my ph in the low 7s, how do i do a water change with out a bad ph swing and killing my fish or hurting my plants? my fish have adjusted to the ph level and are doing fine and there are evening breeding (various tetras) with the higher ph levels. my ph level was 8.1 over a 24 hour period it dropped to 7.9.my fish have not changed they are still very active and doing good.i dont know where to start for a happy medium i am getting all kinds of different answers.how would i do a water change with out getting a ph swing? how much co2 should i be putting in? what ph level should i be going for a planted and live fish tank

1. You could do several things. #1, you could mix some distilled water into the water you intend to add to the tank, as distilled has pH 7 and low KH and GH. #2, you could buy a few bales of peat moss and soak some in the water you intend to add, since peat moss will absorb DIC's and lower your KH and pH, or #3 (recommended), get an RO unit. RO (reverse osmosis) is a fancy water filtration system mostly used for drinking water - it strips the water of all (or most) of the minerals, impurities, and chemicals and is basically a distilled water maker on steroids. Not only will you be able to use an RO unit for your fish, but you'll have some great drinking water, which can also be used in an iron for ironing clothes, haha.

2. If you don't have a drop checker, I would strongly advise you get one. You can use a pH-KH algorithm to check CO2 levels in your water, but it's VERY inaccurate, plus drop checkers can be as cheap as ten bucks shipped. It is THE definitive way to measure whether you're adding enough CO2.

3. It depends on the fish and the plants. Some fish like cichlids like high pH, others like rams and tetras prefer low pH. Most plants prefer low pH, I believe. Do some research on the inhabitants of your tank and determine what pH you should aim for. The easiest way to control pH would be to start with RO water with a neutral pH and either add alkaline buffers to elevate the KH and pH to a target level, or use CO2 to marginally lower the pH (however, watch out for pH swing between day and night!).

Hope this helps!

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Officially fishless until after the move....tune in later for details!

The ph swing is natural and will not hurt your fish. My ph swings a full point from pressurized CO2 and I do 70-80% water changes. I add RO water to mine, but this doesn't matter.....the amount of CO2 added remains constant so my ph still swings the same amount regardless of the starting ph.

Only use a drop checker to confirm CO2 levels. The ph/kh/CO2 relationship chart applies to the solution in the drop checker and not what is in your tank.

I think people sweat ph way too much. Rest assured if you are getting to 7.0 you can have just about anything you want. Any fish - you should properly acclimate them to your water. Do not try to aim for any specific value. Unless you plan to have Discus, don't worry about it. Most importantly, don't use any ph altering chemicals.