Pandas And Sodium Bicarbonate

Hello All,
I am a relative newbie. I mentioned on here earlier that I added 2tsp of baking soda to relieve low KH problems and an impending pH crash. It worked. I also added some finely crushed coral in a bag to the filter. As I approached "double zero", I did 1x50% & 2x66% w/c's to get rid of the baking soda and nitrates. After cycling, I added 5 otos, 5 panda corys, 10 neons and 6 ember tetras in quick succession. The tank (125L) is not overstocked. Each group of fish came from a different LFS. The pandas have never shoaled, and I have recently lost two, with no obvious signs of disease or injury. The other fish are thriving, particularly the otos.
Since cycling, I have a done 17% w/c every 3 days to keep nitrates to 20-40ppm. NH3 & NO2 are zero. I have now discovered from a senior member of staff, that the (panda) supplying LFS uses baking soda to buffer its soft water. Could this be the cause?
                                             Skittler

Thanks Sue,
It was my intention to buy some more today, but then I found the second one dead, so I thought I had better ask the question. As I sit here typing, the remaining 3 are enjoying some catfish pellets, so hopefully they will be OK. I used the LFS in question because it has the same tap water supply as me, whereas the otos came from one with hard water, but kept their otos in an unsightly tank with lots of algae (just like mine was after cycling). We do learn by experience! Thank you for your prompt reply, now off to a "trusted" LFS

                                                   Skittler

Hello Steve,
Yes, you are quite right. I have seen otos and cories in very clean, bare tanks elsewhere. How they sell them I will never know. On the algae wafer problem, I asked the LFS what they fed the otos on, in addition to the algae in the tank. He said he uses Tetra Pleco Multi Wafers, which I bought (inevitably!). He told me to add one at "lights out", so that the other fish don't get there first, which I have been doing occasionally. It is a "2 in 1" wafer, with an algae disc in the centre. They loved the algae disc, but left the rest, which was removed. Now, I break it up and just give them the middle bit. The plan is to have an algae "standby" for when they have cleaned the tank. They are doing a first class job, and are incredibly active at night, but still have some way to go. Thanks for all the wonderful advice, this site is a first class education in fish keeping.

                                                                            Skittler

Thanks Sue,
I will try that when the sun appears. My odd little bungalow has only two windows, and both are north facing. So, I will perhaps try a covered jar outside.

Steve,
Another thought about feeding otos. I am watching my increased group of pandas enjoying some New Era catfish pellets.......together with 3 of the otos!  Whilst the composition includes algae, it also says "43.7% protein". I am sure that I have read somewhere that otos may not be able to digest protein......somebody ought to tell this crew. When I add the pellets, they leave the algae on the glass, and head for the pellets! Perhaps it's like ice cream and children......
                                                 Thanks for your responses,
                                                                 Skittler