Salifert problem, PH advice

[Steviet]

I bought a new Salifert test kit to replace my old one thats used up now, the new kit measured Cal at 440 today, the old kit measured it at 395 yesterday. Both kits are within date and I added only 5gm Bicarb between tests. Old kit 12-2013 new kit 03-2015.
Thats a massive difference between the same tests from the same manufacturer

Also my parameters are pretty stable and I know how much to add daily to adjust KH and Cal (cal may be in question now ), PH is always around 7.8 -7.6 and I know KH is falling when the pH begins to fall, however is it worth buffering PH upwards when I know its stable.
The only reason for asking is because when introducing a new inhabitant it could be quite a difference between the old water and my tank. I know gradual acclimatisation is always the answer but thats not always possible in an emergency.

[Norvern Rob]

Firstly, 395 or 440 are both fine, you could up it a little bit so it reads 450-460 on the higher test, then if the lower one is right you're still over 400. Have you tried repeating the tests 3 times with each kit and seeing what you get each time?

Secondly, your PH is low, 7.6 is unusual IME. Has your tank got a lid, is the water surface turbulent, skimmer working properly etc? What test kit is it? TBH I don't bother testing PH, I have lots of surface movement and have the windows in the room the tank is in open most of the time (in a closed room CO2 build up from us breathing etc can lower PH to some extent) so there's not much else I can do anyway.

Keep your dKH around 9-10 and make sure you've got plenty of surface movement, then I wouldn't worry about the PH if everything in the tank is fine, i'd be suprised if it is actually 7.6 with those parameters.

As for acclimatising new inhabitants, then IME fish aren't really bothered, I take no more than 15-20 mins to acclimatise them and never have a problem. Inverts I always drip for 2 hours+ so that's a nice gradual change even if the parameters are well apart to start with (quite possible as LFS salinity is often lower than our tanks).

[Linda]

I'd be suspicious of the pH test kit. I run my tank with glass covers to stop jumpers, in a room with the windows closed, and mine is always around the 8.2/8.3 mark with the kH at 10. It only drops if the kH drops

As Rob said, I would try several repeats with both kits. I sometimes get a whacky reading from the mag kit, but if I repeat it it always turns out to be a one off fluke

[Steviet]

Unfortunately I cant repeat the test with the old kit as its run out but I will test again with the new one.

The tank has an open top and a 6100 points slightly upwards, and the window is open throughout the day. PH is monitored with a calibrated Pinpoint PH probe which is about 6 months old now and was last cleaned 2 weeks ago. Ph is very stable. Using the Salifert PH test it reads 8.3 which is what I would expect

KH is usually around 8 so I will up it to 9-10 over the next few days and see what happens, on the odd occasion its been up to 9.6 the PH was only 7.67. I can up the PH if its needed but I havent so far because everything else is good.

[Linda]

I wouldn't worry too much about it. It's better for it to be stable than high.

[greg.lynes]

I bought a new calcium test kit a couple of weeks ago and had the same results. The new kit was giving a much higher reading than the previous one 480ppm .