Added several pieces of bogwood to both my tanks and deep cleaning my 17L.

Guessing I won't see a change in ph for atleast a week?

Adding bog wood alone will not drop the PH by a great amount. It also depends on the type of wood that is used and many other factors. Your PH will not be stable either as the amount of tannins released from it is never the same from one day to another. The only way really of doing this, especially from a high ph of which you are starting with, is, as EagleC says, is to add RO water in with your tap water. If you cant afford your own RO unit you can buy the water from your local Aquatic centre, such as Maidenhead Aquatics if you have one or somewhere similar.

On the subject of the 17litre I will say again, please do not use it, if you do you will be in breach of the Animal welfare act, this states that you are obligated to provide -

a suitable environment (how it is housed);
a suitable diet (what it eats and drinks);
the ability to exhibit normal behaviour patterns;
any need it has to be housed with, or apart from, other animals; and
protection from pain, suffering, injury and disease -

None of which will be satisfied if you put any fish in that tiny tank. The water volume is too small to control and will cause your fish suffering, no matter how many water changes you do. More so considering the problems you are already experiencing with your PH. If you put any fish in that 17litre tank you will be in breach of this act. No fish can thrive in a tank smaller than 45 litres.

The 17L is going to be used as a plant and shrimp tank, going to get a much larger tank to section off for bettas.

My lfs sells RO Water 25L for a £1, so will see how the bog wood effects, and try that, more worried about ph shocks.

OK, Shrimps are good.

If you use RO water you are less likely to get PH shocks than you are with Bogwood. As I said Bogwood is not going to give you a stable PH. When you do the water changes even at 10% it is going to push the PH back up and will affect the buffering of the wood, whereas adding RO will give you the ability of adjusting the PH before putting it into the tank. Reducing PH and keeping it stable is a lot harder than raising it. You also need to keep an eye on your KH as this directly affects the ph in your tank, so a KH test kit is necessary. You will need to reduce you PH before putting it into the tank, and you cant do that with bogwood alone, especially not at the levels you are working with.

So, if I were to get the RO Water (sold at £1 for 25L at my lfs) would I just use it along with my normal water changes, 50% RO to 50% tap water + dechlorinator to all. Or would I need to experiment with the proportions to get the required ph? Also, have to acclimitise all of the fish I have in my tank as if they were new?

As everybody's water is different you will need to experiment to see what is best for you. And yes you would have to lower the PH very slowly over several weeks if not months before you get it down to the required PH. Never try to rush the lowering of PH.

You don't need to dechlorinate the RO water btw, the process has removed chlorine along with everything else

just a quick paranoia note about shop bought RO water.

We've had several people suffer tank disasters where for whatever reason the shop bought RO water was not what is was supposed to be.

Either the shop did not maintain the filter and sold tap water as RO water or when adding minerals or marine salts got confused and added the wrong one or the wrong quantity. I'm sure you can imagine the devastating result of doing a 20% water change with seawater in a freshwater tank!

For this reason I always recommend that people only buy pure RO water and mix the minerals they require themselves. For this to work you need a few things.
1. A TDS meter.
This measures the total disolved solids in water. RO water should have 95% of the TDS of the tap water removed. Tap water should have less than 500ppm TDS so anything over 25ppm TDS has not been properly filtered. The tester is a pen style device that you dip in the water for an instant reading and costs less than £20 from ebay. If the lfs sells RO they should be able to show you the TDS with their tester - but it's a worthwhile investment if you're using RO water.
If the RO water is DI filtered then the TDS should be zero, this is ideal as without the DI filtering the RO water can still be quite high in phosphates which encourage algae. Getting back to the point, you need to use a TDS so that someone elses error doesn't cause you problems.

2. A KH/GH test kit. So you know where you are. Initially you'll be doing multiple tests on the premixed water as you add a bit of tap, a bit of minerals and a bit of RO again and again working out the right ratios to get the water your fish need. When you the mix right a 10% water change one or twice a week with that and testing the tank weekly until the PH, KH and GH are where you want them. Then just a test once every week or even fortnight to ensure that things stay level and where you expect.

3. Minerals. You can only get so far mixing RO with tap water, you can change the density of minerals in the water but not the ratio. My tap water has currently 7dGH but 15dKH approx. As I understand it this is due to lots of chalk and very little magnesium. To get this to 4dKH and 8dGH I need to dilute it quite a lot and then add TMC Pro Discus. To keep this acidic I then add blackwater extract and keep a CO2 canister running with a PH controller.

GH is 19
KH is 13

Off the scales both of them. Talked to another lfs today, and their ph is also 8.0, so is it that much of a problem? All my fish seem to be doing well, only ever had one death which was my fighter.

(on a side note I was deep cleaning my tank - the problem one with my fighter, and is now being used as a temp home for 5 WCMMs)

Yes having a ph of 8 can be a problem. If it gets to 9 fish will die. The fighter needs water of PH 6.0 - 6.5 preferably. This is acidic, PH 8 and above is in the realms of baking soda, sea water, and very alkaline. So yes it can be that much of a problem. Ph is exponential in its calculation, this means for every single rise in number is a ten fold rise. I.e 6.0 - 7.0 is 10 times higher, then rise to 8.0 is 100 rise to 9 1000 up to 10 is 10,000 times and so on. So in the case of your fighter your water is approx 100 times to alkaline. Softwater fish cannot handle that level of alkalinity and this causes respirotory problems and also affects the fishes metabolism, eventually leading to premature death. Fish suited to your water are guppies and platties and the likes, or for much bigger tanks, Tangayikan and Malawi cichlids. Ammonia is also more potent at higher PH's so everything is affected by the PH level.

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