u use ada soil? if use ada amazonia 2 ph shud be low...

u have plant anything? have driftwood? maybe u making too much water change. or your stone is leach the alcalic. picture please

btw imho 7.5 is ok. mineral water is 7.5 it will go down in time.
if u are using aqua soil esp the ADA one it will go below 7. i never get 7.

actually the best practise is to let the water tank cycle complete before put the fauna in the tank.

RM30+
emm what do u have in the filter? carbon? bio ring? some says they can lower the PH. dont worry. imho that tank is ok

ps. i saw the cardinal.

saw that u stated that u just started the planted tank 1 week ago, does it mean the tank and water just 1 week old?

if yes, ur tetra die because of nitrogen cycle. let your tank cycle atleast for a month then u can put fauna inside. or u can put fauna earlier, but do expect it to die as new aquarium is full of toxic.

please read more on aquarium nitrogen cycle for new tank. read this as a beginning: http://freshaquarium.about.com/cs/biologic...trogencycle.htm

100% sure your fish died due to ammonia poisoning. Read up more about how ammonia/nitrite/nitrate is produced and how they are poisonous to your fish


p/s: I was like you before, 6 goldfish of mine died after just 5 days, didn't know why, thought it was due to overcrowding But in the end I found out it was about the nitrogen cycle..... basically what your fish excrete (waste, exhalation) kills them..

No worry bro, as i mentioned earlier

"Fish can live in wide range of water ph. As long there is no sudden fluctuation in ph and hardness that most likely to stress them."

And make sure ur water stable. As a beginner, just need to understand nitrogen cycle in tank, regarding the ph, as long it is stable, that is good enough for the fish.

Bro, wanna ask. Is your tank fully cycled already?

Btw, slight fluctuations in pH is generally fine

yup, but as long u are not change the whole water, then it is ok. just do around 20% -30% water change every 3 days for new tank for the first month. then just change 10% once a week after the nitrogen cycle completed, to maintain the stabled water.

as bro -kytz- said, slight fluctuations in pH is generally fine

that what i did to my tank. i have 0 casualties, but 1 of my zebra danio died because he jumped out from the tank lol.

now i didnt do any water change at all coz i know it is already stabled and i have a lot of good bacteria in my filter, just topup water and rinse my filter media only hauhauha, all my fish and now become fat and happy. 
and one more thing, please use a good anti clorine/chloramine if u do water changes. do not pour direct water from the tab, coz it contain clorine that kills beneficial bacteria.

A tank takes about 3-4 weeks to completely cycle? Cycling means establishing a bed of bacteria in your tank, usually in the filter media. You can get those test kits from your LFS (local fish store), RM100+ for a complete test kit for Ammonia, Nitrite, Nitrate and PH

Some fish are hardy some are not, that's why most would recommend using hardy fish to start cycling the tank. Or you can try fishless cycling instead but it involves pouring pure ammonia into your tank and testing the water chemistry.

those rm2 anti chlorine usually just remove chlorine not chloramine. u can get any water conditioner that stated remove chlorine and chloramine such this http://www.apifishcare.com/Products/Produc...px?ProductID=46 or can get any cheaper one in LFS, as long it stated remove chlorine and chloramine, that's good enough

as long the fish still healthy and happy, u are good to go, just maintain the water. while wash ur filter, dont do it thoroughly, just rinse with the tank water or tab water that have been treated with the water conditioner, because u dont want to kill the beneficial bacteria from the filter media. That is the primary reason to have filter media which is to have a colony of bacteria that helping to keep the water stable for fish to live in.
fyi, i never have/buy test kit. I just do it, and trust the nature to take care of everything (plant, bacteria, fish).
another good article, at the last para, he listed what you shouldn't do

http://freshwater-aquarium-passion.blogspo...or-dummies.html

boil it, then if float again, lock it with something heavy.

they have otto or not? hahaha

putrajaya got one..sisaiko...
SK got weijie
PJ got sunwaymas petsmart/fishdepot/fishparadiseBU/ikea/petsfamily taman megah
bangsar midvalley

i bought 230++...mine is small one..1litre...now looking for solenoid..waiting for gaji in..wakakkaa...

so far..i bought it on january..havent refilled it yet..i guess i will be refilling it for the first time on april;..plus i am using it on manual regulator...

i helped him to order from weijie. if ur interested i recommend u try to PM him. very good seller with very very very cheap price

hw much ur budget?