I've been an aquarium hobbyist for a long time.  After a ten year hiatus or so now, I'm finally getting back into it.  Which is to say I've forgotten a lot, and when I went to the pet store, there are a lot of new products out. I've had several planted community tanks but I have never had a "goldfish" tank before.

We have plans for a 50 -100 gallon tank in the future. I have a 10 gal tank with 2 fantails and one live plant. I used some planting substrate that I kept from 10 years ago, along with a layer of sand, and med/large size gravel for the bottom, takes up about a half inch altogether. I have an external filter strong enough for a 20 gallon tank and a 6 inch bubble wand.

I recently learned not to use well water...too hard!!! and buffers out anything I put in it to lower pH or soften the water... so I moved to bottled RO water (7.0pH)....pH did not spike as quickly, but within a week rose to a dark 7.6.   So now I tried a little  distilled water, changed 1 1/2 gallons with distilled water (6.5 pH)...but after a few hours, and filtering still 7.6...

 My fantails are happy colorful and active, don't seem effected... My goal is to put a few more plants in, but don't want to put anything new in until the pH is lower and consistent... I also have a green and brown algae problem. 

How can I lower the pH and how often do I need to change the water? any product recommendations for getting rid of the algae? how tolerant are fantails of pH etc?

Fantailer summed it up nicely
But I've got a few points for you: Leave the pH alone. It's perfect. Adding more live plants will absorb nitrates as nutrition, competing with the algae naturally. If you're keeping the tank light on for longer than 10-12 hours, try decreasing it, since algae thrive in a well-lit environment!
You're probably familiar with the nitrogen cycle and water testing since you said you've kept fish before? Do you regularly test the ammonia, nitrite and nitrate too?

Any pH below 6.4 is too low. Ive heard putting a bit of baking soda in the water makes the pH go up.

thanks fantailer and Nossie... very helpful!  I haven't tested for nitrates or ammonia yet, I'm waiting for my super duper testing kit to  come in the mail... the pet stores near me are mostly over priced and they don't have a good selection.
 

got my testing stuff!   and... my pH is more whacked than I thought... I actually had to use the higher pH test to figure out what it was... its 8.2!!!   yikes! um, everything else tested good though, no nitrates, no ammonia...

anyone have experience using peat moss to bring down pH?

okay, thanks. Yeah the fantails seem completely happy, doesn't seem to bother them at all.  Like I said, I've never had goldfish before, and your input is very helpful.  Now that I have a stable pH, I'm going to put some more plants in, being mindful of the high pH... finding plants that will tolerate that... I found a great article,( since I'm a new member, the forum won't let me share it...) its titled ' plants in the goldfish tank' by Jennifer Greene...(case anyone wants to google it)  I've found a few plants from that article that tolerate high pH...that I think I will try... later and thanks...

 

I have to bring the PH up slightly in the rainwater water I use  for water changes... and fantailer is right, baking soda works fine (and you dont need much) also its cheap and not nasty... cheers >Ron