PH levels

between what PH levels are fire bellies happy, does it have to be exactly newt-ral 7? theyve been in a smaller tank for just over 1 week, while the big one establishes nitrate cycle, the ph level in the little one is 7 and they are happy in there for now, but the level in the big one went from 7.7 to 6.4, is this upi-downi ness a to be expected while the tank stabilises?

There are various reasons for pH to fluctuate in an aquarium. Live plants can change it, and the process of decay produces acidity, which makes pH go down over time (but not usually as fast as you have seen).

Do you have soft water (low mineral content)? If so, I would recommend adding some kind of calcium carbonate to your tanks, as it will buffer against dropping pH. You can use limestone rock, calci-sand (sold for reptiles), bird grit, or crushed shells.

I don't think anyone knows for sure what the pH preference is for firebellies. But they have been kept successfully from 6.0 to 8.0. What you really do NOT want, is for the pH to fluctuate rapidly, even within this range.

i do have various different plants in there, and underneath the gravel is plant substrate, as i thought they liked a few plants, which they will need to lay eggs in too, maybe i should stick to one kind of plant, what would be the best kind? im not sure about the water, i put 'aquasafe' in it to turn tap water into aquarium water, is this soft water?

Sometimes when you add conditioner to the water and/or let water sit in an aquarium for a while, the pH will change from what it was when it came from the tap. This is normal. The hardness won't change, though.

Having "soft water" means that you don't have much natural minerals (calcium and magnesium, mostly) in the water. There is nothing you can add to the water that will make it soft. If you don't know whether your local water is soft or hard, the best way to find out would be to ask around. A local pet store may be able to tell you (if you find an experienced employee), or you can ask your local waterworks.

The advantage of having hard water is that the natural minerals prevent the pH from changing much. If you have soft water, then you need to check the pH more often.

What is the plant substrate that you have under the gravel? If this contains some fertilizer, it might affect your pH. I wouldn't worry about the plants themselves, unless they start to decay.

i found out it is medium to soft, so if i get some reptile sand instead of the gravel and put normal pond weeds in with that, take out my tropical plants, i should be ok, i don't know if the substrate contains fertiliser, it was like kind of dry pieces of light browny breakfast cereal, i also put in little nitrate minus balls amongst the gravel to help maintain PH and control algae, is this ok?
you may have seen i made another string, u can reply on either this one or that one or both, much appreciated jen

Don't use a whole tankful of the calci-sand! It could make the pH too high (and/or too different from your tap water). Just add a bit. When I lived in a soft water area, I just kept a couple of tablespoons full of the calci-sand in each of my filters.